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SUMMARY 


COURSE  OF  PERMANENT  fORTIFICATION 


AND    OF    THE 


Attack  and  Defence  of  Permanent  Works. 


FOR    THE    USE    OP   THK 


CADETS    OF    THE    U.  S.  MILITARY    ACADEMY. 


BY  D.  11.  MAHAN, 


PROFESSOR  OF  MIMTAHY  KNGINKKIUNO,  ETC..  KTC. 


CHARLESTON : 

S  T  E  A  M  -  r  O  \N'  K  li     I'  K  K  8  S  E  S     OF     EVANS     Si     C  O  G  S  \V  E  L  I, 
No.  .S  Broad  ami  lO.T  East  Bay  Street. 

18C2. 


PREFA^CE. 


HEAD-QUARTERS, 

Military  District  South  Carolina. 
Charleston,  1862. 

The  following  work  is  published  tVom  the  lithographic  copy 
of  the  treatise  on  "  Permanent  Fortification,  and  Attack  and 
Defence  of  Fortified  Places,"  taught  at  the  United  States  Mili- 
tary' Academy,  under  D.  H.  Maiian,  Professor  of  Civil  arid 
Military  Engineering. 

It  is  believed  that  it  contains  all  which  it  was  in  the  power 
of  the  distinguished  compiler  to  include  up  to  the  j-ear  ISfiO, 
and  that  it  has  everything  relating  to  those  subjects  taught  at 
Metz.  in  the  French  School  of  Engineers,  to  the  same  date. 

R.  S.  IIIPLEY, 

Brigadier- General  (Commanding. 


Digitized  by  the  Internet  Arciiive 
in  2010  with  funding  from 
Duke  University  Libraries 


http://www.archive.org/details/summaryofcourseOOmaha 


TABLE   OF  CONTENTS. 


PA«K. 

System  of  Fortification  Drawing 7 

Permanent  Fortification 35 

Component  Elements  of  Permanent  Works 3(! 

Open  Defences 48 

Covered  Defences 52 

Communications 69 

Elements  of  the  Plan  of  Enceintes  and  Outworks   73 

Outworks  and  Detached  Works 75 

Interior  Retrenchments 7!j 

Bastioned  Systems 81 

Vauban's  1st  Method 83 

Vauban's  3d  Method 90 

Cokmontaingne's  Method 94 

Methods  of  the  Schools  of  Mezieres  and  Metz 101 

Noizet's  Method 1 02 

CiiAssELOUp's  Method 150 

Haxo's  Method 154 

Choumara's  Method I5S 

Coehorn's  Method 10  7 

Tenailled  System 1 73 

Carnot's  Tenailled  Mktiiod 1  74 

Polygonal  System 17  7 

Montalemrert's  Polygonal  Method 17,s 

Uecent  German  Fortifications 181 

Fronts  of  Posen 191 

Fort  Alexander. 19.S 

Work  at  Germersheim 1 9<; 

(Jerman  Forts 20'2 

Adaptation  of  Permanent  Fortification  to  the  Topographi- 
cal Features  of  Frontiers 204 

Summary  of  the  Progress  of  Fortification 21.S 

Progress  of  the  Attack  since  the  Invention  of  Firearms  .  .22<! 
Influence  of  Irregularities  of  Site  on  Permanent  Works.  .231 

Mines 25<» 

Attack  and  Defence  'ov  Permanent  Works 292 


S  XT  M  ]Vi:  A.  R  Y 


COURSE  OF  PERMANENT  FORTIFICATIONS 

AND    OF    THK 

ATTACK  &  DEFENCE  OF  PEKllANEN T  WORKS 


^D.'itcjn  of  ^ortifiqatimi  tlriunng. 


l...The  method  now  in  general  use,  among  military 
engineers,  for  delineating  the  plans  of  permanent  fortifi- 
cations, is  similar  to  the  one  which  had  heen  previously 
employed  for  representing  the  natural  surface  of  ground 
in  topographical  and  hydrographical  surveys;  which  con- 
sists in  projecting,  oti  a  horizontal  plane,  at  any  assumed 
level,  the  hounding  lines  of  the  surfaces  and.  also,  tin- 
horizontal  lines  cut  from  them  by  equidistant  horizontal 
planes;  the  distances  of  these  lines  from  the  as.sunied 
plane  being  expressed  numerically  in  terni>  of  some  linear 
measure,  as  a  yard,  a  foot,  etc. 

2. ..Plane  of  TJefeuence,  or  Comparison.  The  assumed 
horizontal  plane,  upon  which  the  lines  are  projected,  is 
termed  the  phmc  of  comparison  or  phivc  of  rrfrrcvre,  as  it  is 
the  one  to  which  the  distances  of  all  the  lines  from  it  are 


8  SYSTEM    OF    FORTIFICATION    DRAWING. 

referred,  and  as  it  serves  to  compare  these  distances  with 
each  other,  and  to  determine  the  relative  positions  of  the 
lines. 

3... References.  The  numbers  which  express  the  dis- 
tances of  the  lines  from  the  plane  of  comparison,  are 
termed  references.  The  unit  in  which  these  distances 
are  expressed,  is  usually  the  linear  foot  and  its  decimal 
divisions. 

As  the  position  assumed  for  the  plane  of  comparison  is 
arbitrary,  it  may  be  taken  either  above  or  below  every 
point  of  the  surface  to  be  projected. 

In  the  French  military  service,  it  is  usually  taken  above; 
in  our  own,  below  the  surface.  The  latter  seems  the  more 
natural  and  is  more  convenient,  as  vertical  distances  are 
more  habitually  estimated  from  below  upward  than  in  the 
contrary  direction.  Each  of  these  methods  has  the  advan- 
tage of  requiring  but  one  kind  of  symbol  to  be  used,  viz  : 
the  numerals  expressing  the  references;  whereas,  if  the 
plane  of  comparison  were  so  taken  that  some  of  the  lines 
projected  should  lie  on  one  side  of  it  and  some  on  the 
other,  then  it  would  be  necessary  to  use,  in  connection 
with  the  references,  the  algebraic  symbols  plus  or  minus, 
to  designate  those  lines  above  the  plane  from  those  below 
it. 

This  method  of  representing  objects  has  given  rise  to  a 
very  useful  modification  of  the  ordinary  one  of  orthogonal 
projections  on  two  planes,  and  has  been  denominated  one 
plane  deseriptive  geometry ;  the  plane  of  comparison  being 
the  sole  plane  of  projection ;  the  references  taking  the 
place  of  the  usual  projections  on  a  vertical  plane.  By  this 
modification,  the  number  of  lines  to  be  drawn  is  greatly 
decreased ;  the  complication  of  the  drawing  lessened ;  the 
graphical  operations  required  in  the  solution  of  problems, 
presented  b}'  the  drawing,  simplified ;  and  the  relations  of 
the  parts  more  readily  seized  upon,  as  the  eye  is  confined 
to  one  plane  of  projection  alone.  But  the  chief  advantage 
of  it  consi-sts  in  its  application  to  the  delineation  of  objects, 
like   works    of  permanent   fortification,    where,  .from    the 


SYSTEM    OF    FORTIFICATION    DRAWING.  9 

great  disparity  of  tlic  liorizontal  extent  covered,  and  the 
vertical  dimensions  of  the  parts,  a  drawing,  made  to  a  scale 
w^hicli  would  give  tlie  horizontal  distances  with  accuracy, 
could  not,  in  most  cases,  render  the  vertical  dimensions 
with  an}^  a})proach  to  the  same  degree  of  accuracy ;  or,  if 
made  to  a  scale  which  would  admit  of  the  vertical  dimen- 
sions being  accurately  determined,  would  require  an  area 
of  drawing  surface,  to  render  the  horizontal  dimensions  to 
the  same  scale,  wdiich  would  exceed  the  convenient  limits 
of  practice. 

Taking,  for  exnnqde,  an  ordinar}^  scale  used  for  drawing 
the  jdans  of  permanent  fortifications  o^  07tc  inch  io  fifty  feet, 
or  the  scale  gJ-^,  the  details  of  all  the  bounding  surfaces 
can  be  determined  with  accuracy  to  within  the  fraetional 
part  of  a  foot;  whereas,  a  vertical  projection  to  the  same 
scale  would  be  altogether  too  small  for  the  same  purjjoses. 

The  reference  of  any  point  or  line  of  the  plane  of  refer- 
ence will,  therefore,  be  zero;  that  of  any  point  above  it 
will  be  expressed  in  feet,  decimal  parts  of  a  foot  being 
used  whenever  the  reference  is  not  an  entire  number.  In 
writing  the  reference  the  mark  used  to  designate  the  linear 
unit  is  omitted,  in  order  that  the  numbers  expressing 
references  may  not  be  mistaken  for  those  which  may  be 
put  upon  the  drawing  to  express  the  horizontal  distances 
between  points. 

The  Inferences  of  horizontal  lines  are  written  u}>on  the 
projections  of  these  lines.  All  other  references  are  written, 
as  nearly  as  })racticable,  parallel  to  the  bottom  border  of 
the  drawiui?,  for  the  convenience  of  readinti;  them  without 
having  to  shift  the  position  of  the  sheet  on  which  the 
drawing  is  made. 

4. ..Point  and  Right  Line.  To  designate  the  position 
of  a  point,  PI.  1,  Fig.  1,  the  projection  of  the  point  and 
its  reference  are  enclosed  within  a  bracket,  thus:  (28,50). 
This  expresses  that  the  vertical  distance  of  the  [)oint  from 
the  })lane  of  reference  is  2S  feet  and  /g"^  of  a  foot.  The 
positio-n  of  a  right  line,  oblicpie  to  the  }»lane  of  reference, 
is  designated  by  the  projection  of  the  line,  and  the  refer- 


10  SYSTEM    OF    FORTIFICATION    DRAWING. 

ences  of  any  two  of  its  points.  Thus,  in  Fig.  1,  the  points 
a  and  6,  upon  the  projection  of  the  right  line,  witli  their 
respective  references,  (25,15)  and  (28,50),  determine  the 
position  of  the  line  with  respect  to  the  plane  of  reference. 

When  the  line  is  horizontal,  or  parallel  to  the  plane  of 
reference,  its  projection,  with  the  reference  of  one  of  its 
points,  will  be  sufficient  to  designate  it,  and  fix  its  posi- 
tion witli  respect  to  the  plane  of  reference.  Thus,  in  Fig. 
1,  the  reference  (25,15)  written  upon  the  projection  of  the 
line,  expresses  that  the  line  is  horizontal,  and  25,15  feet 
from  the  plane  of  reference. 

5. ..For  the  convenience  of  numerical  calculation,  the 
position  of  a  line,  with  respect  to  the  plane  of  reference,  is 
often  expressed  in  terms  of  the  natural  tangent  of  the  angle 
it  makes  with  the  plane ;  but  as  this  angle  is  the  same  as 
that  between  the  line  and  its  projection,  its  natural  tangent 
can  be  expressed  by  the  difference  of  level  between  any 
two  points  of  the  line,  divided  by  the  horizontal  distance 
between  the  points.  Now,  as  the  difference  of  level  be- 
tween any  two  points  of  the  line  is  the  same  as  the  differ- 
ence of  the  references  of  the  points,  and  the  horizontal 
distance  between  them  is  the  same  as  the  horizontal  pro- 
jection of  the  portion  of  the  line  between  the  same  points, 
it  follows,  that  the  natural  tangent  of  the  angle  which  the 
line  makes  with  the  plane  of  reference  is  found  by  dividing 
the  difference  of  the  references  of  the  points  by  the  dis- 
tance in  horizontal  projection  between  them. 

The  vulgar  fraction  which  expresses  this  tangent  is  term- 
ed the  inclination,  or  declivity  of  the  line.  Thus,  the  fraction 
\  would  express  that  the  horizontal  distance  between  any 
two  points  is  six  times  the  vertical  distance  or  difference  of 
their  references;  the  fraction  f,  that  the  vertical  distance 
between  any  two  points  is  two-thirds  of  the  horizontal  dis- 
tance; the  dcyiominator  of  the  fraction,  in  all  cases,  rejyrcsenting 
the  number  of  parts  in  horizontal  projection,  and  the  numerator 
the  corresponding  number  of  parts  in  vertical  distance. 

When  the  position  of  a  line  is  designated  in  this  way,  it 
is  said  to  be  a  line  whose  inclination,  or  declivity,  is  one- 


SYSTEM    OF    FORTIFICATION    DRAWING.  11 

sixth,  two-thirds,  ten  on  one,  etc.,  or  simply  a  line  of  one- 
sixth,  etc. 

6... When  the  projection  of  a  line  is  divided  into  equal 
parts,  each  of  which  corresponds  to  a  unit  in  vertical  dis- 
tance, and  the  reference  of  the  points  of  division  are  written, 
it  is  termed  the  scale  of  declivity  of  the  line.  In  constructing 
the  scale  of  declivity  of  a  line,  the  entire  references  are 
alone  put  down ;  one  of  the  divisions  of  the  equal  parts 
heing  subdivided  into  tenths,  or  hundredths  if  necessary, 
so  as  to  give  the  fractional  parts  of  the  references  corre- 
sponding to  any  fractional  part  of  an  entire  division. 

7... Having  the  inclination  of  a  line,  the  difference  of 
reference  of  any  two  of  its  points,  the  projections  of  which 
are  given,  will  be  found  by  multiplying  the  horizontal  dis- 
tance between  them  by  the  fraction  which  expresses  this 
inclination ;  in  like  manner,  the  horizontal  distance  of  any 
two  points  will  be  obtained  by  dividing  the  difference  of 
their  references  by  this  fraction. 

To  obtain,  therefore,  the  reference  of  a  point  of  a  line, 
having  its  projection,  the  horizontal  distance  between  it 
and  that  of  some  other  known  point  of  the  line  must  be 
determined,  from  the  scale  of  the  drawing  by  which  the 
horizontal  distances  are  measured ;  this  distance  expressed 
in  numbers,  being  multiplied  by  the  fraction  which  ex- 
presses the  inclination  of  the  line,  will  give  the  difference 
of  reference  of  the  two  points ;  the  required  reference  of 
the  point  will  be  found  by  subtracting  this  product  from 
the  reference  of  the  known  point,  if  it  is  higher  than  the 
one  sought,  or  adding  if  it  is  lower.  Thus,  let  (25,15)  be 
the  reference  of  a  known  point  higher  than  the  one  sought; 
the  distance  between  the  points  being  35,57  feet,  and  the 
inclination  of  the  line  ,'g  ;  then,  35,75Xt'(5=3,575  will  be 
the  difference  of  reference  of  the  points,  and  25,15 — 3,575 
=21,575,  the  required  reference.  The  converse  of  this 
shows  that  the  horizontal  distance  between  two  points  on 
this  line,  whose  difference  of  reference  is  3,575,  will  be 
3,575-- ,'o=35,75  feet. 

8... The  true  length  of  any  portion  of  a  line  between  two 


12  SYSTEM    OF    FORTIFICATION    DRAAVINO. 

given  points  is  evidently  the  hypothenuse  of  a  n<>:]it-angle 
trianirle.  of  Avhicli  the  otlior  two  sides  arc  the  difference  ot 
reference  of  the  jioints,  and  their  liorizontal  distance. 

9. ..Plane.  The  iiosition  of  a  i)lane  obliqne  to  tlic  plane 
of  reference,  may  be  determined  either  hy  the  pr(»jcctions 
and  references  of  three  of  its  points  ;  hy  tlie  projections 
and  declivity  of  two  lines  in  it  obliqne  to  the  plane  of 
reference;  or  by  the  projection  of  two  or  more  horizontal 
lines  of  the  plane,  with  their  references. 

The  more  usual  method  of  representing  a  plane  is  by 
the  projections  on  the  plane  of  reference  of  the  horizontal 
lines  determined  by  intersecting  it  by  equidistant  horizon- 
tal planes.  These  lines  are  termed  horizontals  of  the  plane, 
those  usually  being  taken  the  references  of  which  are  entire 
numbers. 

10. ..If,  in  a  plane  given  by  its  horizontals,  a  line  be 
(liawn  perpendicular  to  the  horizontals,  its  projection  on 
the  iilane  of  reference  will  be  also  perpendicular  to  the 
projections  of  the  horizontals.  The  angle  of  this  line  with 
the  i»lane  of  reference  is  evidently  the  same  as  that  of  the 
given  plane  with  it,  and  is  greater  than  tlie  angle  between 
any  otlier  line  drawn  in  the  plane  and  the  plane  of  refer- 
ence. This  line  is,  on  this  account,  termed  the  line  of  great- 
est dedivi///  of  the  plane. 

11...  If  the  scale  of  declivity  of  the  line  of  greatest  de- 
clivity is  constructed,  it  will  alone  serve  to  fix  the  position 
of  the  plane  to  which  it  belongs,  and  to  determine  the  re- 
ference of  any  })oint  of  the  plane  of  which  the  projection 
is  given.  For  the  inclination  of  this  line  and  that  of  the 
plane  are  the  same ;  and  as  the  h(»rizontals  are  perpendicu- 
lar to  the  line  of  greatest  declivity,  the  point  where  the 
horizontal  drawn  through  the  given  projection  of  a  point 
in  the  itlane  cuts  this  line  will  determine  upon  the  scale 
the  reference  of  the  horizontal,  and,  therefore,  that  of  the 
point. 

12. ..The  inclination,  or  declivity  of  a  plane  with  the  [dane 
of  reference,  may  be  expressed  in  the  same  way  as  the  incli- 
nation  of  its  line  of  greatest  declivity.     Thus:  a  plane  of 


SYSTEM    OF    FORTTFir-ATIOX    DRAWING.  13 

one-fourth^  a  plave  of  tirrnt)/  ov  one,  a  plane  of  Uro-ihirds, 
express  that  tlie  natural  tano;ent  of  the  angle  between  the 
planes  and  the  [)lane  of  reference  are  respectively  repre- 
sented hv  the  fractions  i,  Y  and  |. 

13... The  horizontal  distance  between  two  horizontals  of 
a  plane,  the  angle  of  which  is  given,  can  be  found  in  the 
same  way  as  the  horizontal  distance  between  two  points  of 
a  line,  the  inclination  of  which  is  given,  Art.  7,  by  dividing 
the  difference  of  the  reference  of  the  horizontals  by  the 
fraction  representing  the  inclination  of  the  plane ;  in  like 
manner  the  difference  of  references  of  two  horizontals  will 
be  obtained  by  multiplying  their  horizontal  distance  by  the 
same  fraction. 

14. ..To  distinguish  the  scale  of  declivity,  PL  1,  Fig.  2, 
from  an}-  other  line  of  a  plane,  it  is  always  represented  by 
two  fine  parallel  lines,  drawn  near  each  other,  and  crossed 
at  the  points  of  division,  where  the  references  are  written, 
by  short  lines,  which  are  portions  of  the  corresponding 
horizontals. 

With  the  foregoing  elements,  the  usual  problems  of  the 
right  line  and  plane  can  be  readily  solved. 


PROBLEMS  OF  THE  RIGHT  LD^E  AND  PLANE. 

15...PR0B.  1,  Pl.  1,  Fig.  3.  Having  the  projections  and 
references  of  two  lines  thai  intersect,  to  find  the  angle  between 
them. 

Let  a  6  be  the  projection  of  one  of  the  lines,  the  referen- 
ces of  two  of  its  points  (10,30)  and  (4,90)  being  given  ;  cd, 
the  projection  of  the  other  line,  (10,30)  and  (5,0)  being  the 
references  of  two  of  its  points;  (10,30)  being  the  point  of 
intersection  of  the  two  lines. 

Find  on  each  of  tl;e  lines.  Art.  7,  a  point  having  the  same 
reference  (7,0).  The  line  joining  these  two  points  will  be 
horizontal,  and  projoctcd  into  its  true  length  ;  taking  this 
line  as  the  base  of  the  triangle  of  which  the  other  two  side.s 
are  respectively  the  true  lengths  of  the  portions  of  the  two 


14  SYSTEM    OF    FORTIFICATION    DRAWING. 

given  lines  projected  between  (10,30)  and  (7,0),  Art.  7,  the 
anprlc  at  tlie  vertex  will  be  the  one  required. 

16...1*K0B.  2,  Fig.  4.  Through  a  puint^  to  draw  a  line  par- 
allel to  a  given  line. 

Let  c  (7,50)  be  the  projection  of  the  point;  a  b  that  of  the 
given  line  of  which  the  two  points  (7,0)  and  (9,0)  are  known. 

Through  c  drawing  c  d  parallel  to  a  6,  this  will  be  the 
projection  of  the  required  line ;  and  as  its  declivity  is  the 
same  as  that  of  the  given  line,  it  will  be  only  necessar}'  to 
set  off  from  c  toward  d,  the  same  distance  as  between  (7,0) 
and  (9,0),  to  obtain  a  point  (9,50)  as  far  above  (7,50)  as 
(9,0)  is  above  (7,0). 

17...Prob.  3,  Fig.  5.  Through  a  point  in  a  plane,  to  draio  a 
line  in  the  plane  with  a  given  inclination. 

Let  cdhQ  the  scale  of  declivity  of  the  given  plane,  and  a 
(5,50)  the  given  point ;  and  suppose,  for  example,  that  the 
declivity  of  the  plane  is  |,  and  that  the  declivity  of  the 
required  line  is  y'^. 

Draw  the  horizontal  of  the  plane  (5,50)  which  passes 
through  the  i)oint,  and  any  other  horizontal  as  (7,0).  The 
projection  of  the  rciiuircd  line  will  pass  tlirough  «,  and  the 
portion  of  it  between  the  two  horizontals  will  be  equal,  Art. 
6,  to  the  difference  of  their  references,  or  1.5  feet  divided  by 
the  fraction  which  represents  the  inclination  of  the  required 
line.  Describing,  therefore,  from  a  an  arc,  with  this  dis- 
tance «c,  or  1.5^y'g=15  feet  as  a  radius,  and  joining  the 
point  b,  where  it  cuts  the  horizontal  (7,0),  with  «,  this  will 
be  the  projection  of  the  required  line. 

18...Prob.  4,  Pl.  1,  Fig.  6.  Having  three  points  of  a  plane, 
to  construct  its  horizontals  and  scale  of  declivity. 

Let  a  (12,0),  b  (15,25)  and  c  (15,50)  be  the  three  points. 
Join  the  lowest  with  the  other  two,  and  construct  the  scales 
of  declivity  of  the  lines  of  junction,  Art.  6.  The  lines 
joining  the  same  references  on  these  two  lines  will  be  hori- 
zontals of  the  required  plane.  The  scale  of  its  declivity 
will  be  found  by  drawing  two  parallel  lines  perpendicular 
to  the  horizontals,  and  writing  the  references  of  the  points 
where  the  scale  intersects  them. 


SYSTEM    OF    FORTIFICATION    DRAWING.  15 

19..  Prob.  5,  Pl.  1,  Fig.  7.  To  find  the  horizontals  of  a  plane 
'passed  through  a  given  line  ayid  parallel  to  another  line. 

Let  a  h  and  cd  be  the  projections  of  the  two  lines.  From 
a  point  (10,0)  on  cd  draw  a  line,  Prob.  2,  parallel  to  a  b; 
and  by  Prob.  4,  iind  the  horizontals  of  the  plane  of  this  line 
and  cd;  these  will  be  the  required  horizontals. 

20... Prob.  6,  Pl.  1,  Fio.  8.  To  find  the  horizontals  of  a 
plane  the  declivity  of  which  is  given,  and  which  jMSses  through  a 
given  line. 

Let  bd  he  the  scale  of  declivity  of  the  given  line,  and 
suppose,  for  example,  the  declivity  of  the  line  to  be  ^\  and 
that  of  the  required  plane  to  be  J^. 

Since  the  horizontals  of  the  plane  must  pass  through  the 
points  of  the  line  having  the  like  references,  and  as  the  dis- 
tance in  projection  between  any  two  of  them,  Art  13,  will 
be  equal  to  the  diiference  of  their  references  divided  by  the 
fraction  of  inclination  of  the  i)lane,  it  follows  that,  to  find 
the  one  drawn  through  b  (14,0),  for  example,  it  will  be  sim- 
ply necessary  to  describe  from  any  other  point,  as  a  (12,0), 
an  arc  of  a  circle,  with  a  radius  of  12  feet,  equal  to  the 
quotient  just  mentioned,  and  to  draw  a  tangent  to  this  arc 
from  b.  If  any  other  horizontal,  as  (16,0),  is  required,  which 
would  not  intersect  the  given  line  within  the  limits  of  the 
drawing,  any  two  points,  as  (12,0),  and  (14,0)  for  example, 
may  be  taken  as  centres,  and  two  arcs  be  described  from 
them,  with  radii  of  12  and  24  feet,  calculated  as  above;  a 
line  dj-awn  tangent  to  the  arcs  will  bo  the  required  hori- 
zontal. 

21... Prob.  7,  Pl.  1,  Fig.  0.  Having  the  horizontah,  or  the 
scale  of  decliritg  of  two  planes,  to  find  thrir  intersection. 

Join  the  points  where  any  two  horizontals,  as  (12,0)  and 
(14,0),  in  one  plane  intersect  two  corresponding  liorizontals 
of  the  other,  and  the  line  so  found  Avill  be  the  projection  of 
the  required  intersection. 

22...Wlien  the  horizontals  arc  parallel,  or  when  they  are 
so  nearly  parallel  that  their  points  of  intersection  cannot 
be  readily  found,  the  following  method  may  be  taken  : 
Draw  any  two  parallel    lines,  as  cd,  c' d\  Pl.  1,  Fig.  10. 


16  SYSTEM    OV    FORTIFICATION    DKAAVINU. 

These  may  be  considered  as  the  horizontals  of  an  arbitrary- 
plane  having  the  same  references,  (12,0)  and  (14,0),  as  the 
two  corresponding  horizontals  in  each  of  the  given  planes. 

The  intersections  of  the  horizontals  of  the  arbitrar}'' 
plane  with  those  of  the  given  planes  will  determine  two 
linos,  wliich,  being  the  intersections  of  the  given  planes 
Avith  the  arbitrary  plane,  will,  by  their  intersection  o,  de- 
termine a  point  common  to  the  three  planes,  and,  there- 
fore, a  point  of  the  intersection  of  the  two  given  planes. 
Assnming  any  other  two  parallels,  a  6,  a'  6',  as  the  hoi'izon- 
tals  of  another  arbitrary  plane ;  finding  the  point  o'  com- 
mon to  the  three  planes,  and  joining  o  and  o'  by  a  line, 
this  will  be  the  required  intersection. 

When  the  horizontals  of  the  two  planes  are  parallel,  one 
point,  as  o,  will  be  sufficient  to  determine  the  intersection, 
as  its  projection  will  be  parallel  to  the  horizontals. 

23...PROB.  8,  Pl.  1,  Fig.  11.  To  find  where  a  given  line 
pierces  a  given  plane. 

Through  any  two  points  of  the  line,  having  the  same 
references  (12,0)  (14,0),  for  example,  as  two  horizontals  of 
the  given  plane,  draw  two  parallel  lines,  a  b,  a'  />',  Avhich  may 
be  taken  as  the  horizontals  of  an  arbitrary  plane.  The 
line  of  intersection,  7nn,  of  this  plane  with  the  given  plane 
being  determined,  by  Prob.  7,  the  point  o  where  it  inter- 
sects the  given  line  will  be  the  projection  of  the  required 
point,  the  reference  of  which  can  be  found  from  the  scale 
of  the  plane. 

24... Prob.  9,  Pl.  1,  Fig.  12.  To  draw  from  a  given  point 
a  jyerpendieuhr  to  a  given  plane,  and  find  its  length. 

Let  a  (12,0)  be  the  given  point,  and  the  given  plane  be 
represented  by  its  scale  of  declivity. 

The  projection  of  the  required  perpendicular  will  pass 
through  a,  and  be  parallel  to  the  scale  of  declivity  of  the 
given  plane.  The  angle  which  it  makes  with  the  plane  of 
reference  is  the  complement  of  that  between  this  plane  and 
the  given  plane;  its  tangent,  therefore,  will  be  the  recipro- 
cal of  the  tangent  of  that  of  the  given  plane. 

Drawing,  therefore,  through  a,  the  line  ac  parallel  to  the 


SYSTEM    OF    FORTIFICATION   DRAWING.  17 

scale  of  declivity  ot  the  plane,  and  constructing  its  scale  of 
declivity,  Art.  7,  this  will  be  the  projection  of  the  required 
perpendicular.  The  point  o,  where  it  pierces  the  given 
plane,  is  found  b}"  Prob.  8,  and  its  true  length  by  Art.  8. 

25...  Cur i'cd  and  Irregular  Surfaces. 

All  other  surfaces  may,  like  the  plane,  Art.  7,  be  repre- 
sented by  the  projections  on  the  plane  of  reference  of  the 
curves  or  lines,  cut  from  them  by  equidistant  horizontal 
planes,  together  with  the  references  of  these  curves ;  as 
many  of  these  curves  being  drawn  as  may  be  requisite  to 
determine  all  the  points  of  the  surface  with  accuracy. 

In  the  more  simple  geometrical  surfaces,  a  single  hori- 
zontal curve,  with  the  projection  of  some  point  or  line  of 
the  surface,  will  alone  suffice.  For  example,  the  cone  may 
be  represented  by  the  projection  and  reference  of  any 
curve  cut  from  it  by  a  horizontal  plane,  with  the  })rojection 
and  reference  of  its  vertex;  a  cylinder  by  the  })rojection 
and  reference  of  a  like  curve,  with  the  projection  and  ref- 
erence of  one  of  its  right  line  elements  ;  a  spliere  by  the 
projection  and  reference  of  its  centre  and  that  of  its  great 
circle  parallel  to  the  plane  of  reference. 

26... This  method  of  projection  is  more  particularly  ad- 
vantageous in  the  representation  of  irregular  surfaces, 
which,  like  the  natural  surfaces  of  ground,  for  example, 
are  not  submitted  to  any  geometrical  law,  and  in  solving 
the  various  problems  of  tangent  and  secant  planes  to  sur- 
faces of  this  character.  These  surfaces  can  onl^-  be  repre- 
sented by  the  projection  of  the  horizontal  curves  cut  from 
them  by  equidistant  horizontal  planes,  and  by  substituting 
for  the  zone  of  the  real  surface,  contained  between  any 
two  horizontal  curves,  an  artificial  zone,  subjected  to  some 
geometrical  law  of  generation  which  shall  give  an  approx- 
imation to  the  real  surface  sufficiently  accurate  for  the 
object  in  view.  The  usual  method  of  doing  this  is  to  take 
two  consecutive  horizontal  curves,  as  the  directrices  of  the 
artificial  surface  of  the  zone,  and  move  a  right  line  so  as  to 
intersect  them,  and,  in  each  of  its  consecutive  positions,  be 
perpendicular  to  the  consecutive  tangents  to  one  of  the 
9 


18  SYSTEM    OF   FORTIFICATION    DRAWING. 

curves,  the  upper  curve  being  usually  taken  for  this  last 
condition. 

If,  in  PI.  1,  Fig.  13,  for  example,  (6,0),  (7,0),  etc.,  are 
the  projections  of  the  horizontals  of  a  surface,  the  zone 
between  the  curves  (6,0)  and  (7,0)  may  be  replaced  by  an 
artificial  surface,  the  position  of  the  generatrix  of  which, 
at  any  point  of  the  upper  curve  (7,0),  will  be  determined 
by  constructing  the  horizontal  tangent  at  that  point,  as  a, 
for  example,  and  drawing  a  b  perpendicular  to  it  and  inter- 
secting the  lower  curve.  The  position  of  the  generatrix 
a'  b'  at  any  other  point  a'  is  constructed  in  like  manner. 

27... To  obtain  any  curve  of  the  artificial  zone  intermediate 
to  the  two  directrices,  it  will  be  only  necessary  to  construct 
several  positions  of  the  generatrix,  and  to  find  on  these  the 
points  having  the  same  reference  as  the  required  curve.  The 
horizontal  of  the  surface  (6,50),  for  example,  will  bisect  the 
projections  of  the  generatrix  in  its  various  positions. 


PROBLEMS  OF  IRREGULAR  SURFACES  AND  THE 
RIGHT  LINE  AND  PLANE. 

28...PROB.  10,  Pl.  1,  Fig.  14.  Through  a  given  2mnt,  in  a 
vertical  plane  lohich  intersects  a  surface^  to  draw  a  tangent  to  the 
curve  of  intersection  of  the  ])lane  and  surface. 

Let  a  (5,50)  be  the  given  point,  and  ab  the  trace  of  the 
plane.  The  points  where  this  trace  intersects  the  horizontal 
curyes  of  the  surface  will  be  the  projections  of  points  of  the 
curve. 

Let  any  arbitrary  line,  as  a  c,  be  now  draw^n  through  a, 
and  its  scale  of  declivity  be  constructed ;  and  let  the  hori- 
zontal lines  be  drawn  between  the  points  having  the  same 
references  on  dc  and  ab  where  the  latter  cuts  the  horizon- 
tal curves.  These  horizontals  will  generally  make  different 
angles  with  a  c,  and  the  one,  as  (7,0),  which  makes  the 
smallest  angle  with  it,  toward  the  descending  portion,  will 
determine  on  the  curve  the  tangential  point.  To  show  this, 
construct  the  scale  of  declivity  of  the  line  thus  found,  of 


SYSTEM    OF    FORTIFICATION    DRAWING.  19 

whicli  a  (5,50)  is  the  projection  of  one  point,  and  (7,0),  on 
ah,  the  tangent  point,  another.  This  is  most  readilj'  done, 
bj  drawing  throngh  tlic  points  (10,0),  (0,0),  etc.,  ofar,  lines 
parallel  to  the  horizontal  (7,0),  and  iinding  where  they  in- 
tersect ab,  in  which  the  required  tangent  will  be  projected. 
Comparing  now  the  references  of  the  points  on  the  line  just 
found,  and  assumed  as  the  required  tangent,  with  tlie  refer- 
ences of  the  points  of  the  curve  having  the  same  projection, 
it  will  at  once  be  evident  that  these  two  lines  have  onlv  the 
point  projected  in  (7,0)  in  common,  and  that  every  other 
point  of  the  right  line  is  exterior  to  the  curve,  and,  therefore 
this  line  must  be  tangent  to  the  curve  at  the  point  deter- 
mined as  above. 

20...rROB.  11,  Pl.  1,  Fig.  15.  To  comtnid  the  elements  of  a 
cone  with  a  given  vertex  which  shall  envelop  a  given  surface. 

Let  (10,0),  etc.,  be  the  horizontals  of  the  given  surface  ; 
and  a  (6,0)  the  position  of  the  vertex  of  the  cone. 

From  rt,  draw  a  h,  a  b',  etc.,  as  the  traces  of  vertical  planes 
which  pass  through  the  vertex  and  intersect  the  surface. 
Construct,  by  Prob.  10,  the  tangents,  from  a  to  the  curves 
cut  from  the  surface  by  the  planes  ab,  etc.  These  tangents 
will  be  the  required  elements. 

30... Prob.  12,  Pl.  1,  Fig.  15.  To  find  the  curve  of  inter- 
section of  a  cone  enveloping  a  given  surface  bg  a  horizontal  plane. 

Having  found,  by  Probs.  11  and  12,  the  elements  of  the 
cone,  and  constructed  the  scale  of  declivity  of  each  one,  by 
joining  the  points  o,  o'  o",  having  the  same  reference  as  the 
given  horizontal  plane,  as  (9,0)  for  example ;  this  w^ill  lorm 
a  continuous  line  mo"o'on,  which  will  be  the  projection  of 
the  points  where  these  elements  pierce  the  given  plane,  and, 
therefore,  the  projection  of  the  required  intersection. 

31... Prob.  13,  Pl.  2,  Fig.  1.  A  limited  extent  of  surface 
being  given,  and  a  point  exterior  to  it,  to  find  the  limits  within 
which  2^bi)ics  mag  be  passed  through  this  point  and  lie  above  all 
the  given  smfacc. 

Let  a  (8,0)  be  the  given  point;  (10,0),  (0,0),  etc.,  the 
horizontals  of  the  given  surface,  the  limits  of  which  are  the 
sector  contained  within  the  arc  B  D  C,and  the  two  radii  aB 
nud  a  C. 


20  SYSTEM    OF   FORTIFICATION   DRAWING. 

Taking  a  as  the  vertex  of  a  cone  which  shall  envelop  the 
given  surfiiee,  the  elements  of  this  cone  can  be  found  by 
Probs.  11  and  12.  Any  plane  that  can  be  passed  tangent  to 
this  cone,  and  which  shall  not  intersect  the  surface  within 
the  given  limits,  will  satisfy  the  conditions  of  the  problem. 

From  the  position  of  the  vertex  of  the  cone  with  respect 
to  the  surface,  it  will  be  seen  that  a  horizontal  plane,  passed 
through  the  vertex,  will  cut  from  the  cone  two  horizontals 
a  b',  and  a  h"  (8,0)  [the  first  of  which  will  be  tangent  to  the 
horizontal  curve  (8,0)  of  the  surface,  and  the  second  a  h" 
will  pierce  the  surface,  where  the  limiting  arc  B  D  C  cuts 
the  same  horizontal  curve];  and  that  all  the  elements  pro- 
jected within  the  "angles  Bab'  and  Cab'  will  lie  below  the 
horizontal  plane  (8,0).  Now,  if  the  elements  within  these 
angles  be  prolonged  beyond  the  vertex,  they  will  form  two 
portions  of  cones  having  the  same  elements  as  the  portions 
below  the  vertex;  and  it  is  evident  that  any  plane  passed 
tangent  to  the  lower  portion,  as  b'aB,  within  one  of  these 
angles,  will  leave  this  portion  below  it,  and  the  correspond- 
ing portion,  formed  by  the  prolonged  elements,  above  it; 
and,  in  order  that  this  plane  shall  satisfy  the  conditions  of 
the  problem,  it  must  also  leave  the  portions  of  the  cone 
within  the  angles  b'  a  b",  and  b"  a  C,  also  below  it.  The  same 
reasoning  applies  to  planes  passed  tangent  to  the  portions  of 
the  cone  within  each  of  the  other  two  angles.  It  is,  there- 
fore, evident  that  a  plane,  which  shall  satisfy  the  conditions 
imposed,  must  leave  all  that  portion  of  the  cone  which  lies 
above  the  horizontal  plane  (8,0)  through  the  vertex  below 
it,  and  all  the  prolonged  portions  corresponding  to  the  por- 
tions below  the  plane  (8,0)  above  it. 

To  find  any  such  plane,  let  the  cone  be  intersected  by  a 
horizontal  plane,  as  (9,0),  by  Prob.  12.  This  plane  will  cut, 
from  the  portion  of  the  cone  within  the  angle  b'a  b",  a  curve 
of  which  non'  is  the  projection ;  the  two  extreme  points  of 
this  curve,  within  the  limits,  being  at  the  points  where  the 
horizontal  (9,0)  of  the  surface  cuts  the  limiting  arc ;  it  will 
also  cut,  from  each  of  the  prolonged  portions,  a  curve,  the 
one  m  r,  and  the  other  m'  r';  the  extreme  point  m  of  m  r 


SYSTEM    OF    FORTIFICATIOX    DRAWING.  .        21 

being  on  the  prolongation  of  the  extreme  element  a  C ;  that 
m'  of  the  other  on  the  extreme  element  aB,  on  the  other 
side,  prolonged.  Having  obtained  these  three  curves,  let 
tangent  lines  be  drawn  from  the  points  m.  and  m'  to  the 
curve  n  o  n'.  A  plane  passed  through  either  of  these  tan- 
gents and  through  the  corresponding  element  of  the  cone 
as,  or  as',  drawn  through  the  tangential  point,  will  be  a 
tangent  plane  to  the  cone;  and  as  either  of  these  planes 
will  leave  the  curve  non'  on  one  side  of  it,  and  the  two 
curves  mr  and  in' r'  on  the  other,  it  will  leave  all  the  por- 
tion of  the  cone  corresponding  to  the  first  curve  below  it, 
and  the  portions  corresponding  to  the  other  curves  above  it; 
and  will,  therefore,  satisfy  the  required  conditions.  The 
same  will  hold  true  for  any  tangent  plane  to  the  cone  along 
an}'  element  drawn  between  the  points  5  and  6';  since  the 
tangent  drawn  to  any  point  of  the  curve  non',  between  the 
points  s  and  s',  will  leave  this  curve  on  one  side  of  it,  and 
the  other  two,  mr  and  ni'  r',  entirely  on  the  other. 

The  two  horizontal  elements,  a  b'  and  a  h"  of  the  cone, 
will  be  parallel  to  the  assymptotes  of  the  curve  non' ;  and 
their  lines  of  prolongation  beyond  the  vertex  will  be  par- 
allel, in  like  manner,  to  the  assymptotes  of  the  two  curves, 
mr  and  m' r'. 

32...PROB.  14,  Pl.  1,  Fig.  16.  Through  a  given  line,  to  pass 
a -plane  tangent  to  a  surface. 

1st.  Let  a  6  be  the  projection  of  the  given  line,  and 
(10,0),  (0,0),  etc.,  the  horizontals  of  the  surface.  From  the 
points  on  the  line,  as  (10,0),  etc.,  draw  lines  tangent  to  the 
horizontal  curves  having  the  same  references;  the  tangent 
which  makes  with  the  projection  of  the  line  the  least  angle 
toward  the  descending  portion  will,  with  the  line,  deter- 
mine the  required  plane. 

For,  let  the  horizontal  tangent  (10,0)  be  the  one  which 
makes  with  af>  the  least  angle;  from  the  other  points,  (0,0), 
etc.,  of  at),  draw  lines  parallel  to  the  tangent  (10,0); 
these  lines  will  lie  in  the  plane  that  contains  this  tangent 
and  ab,  and  will  be  horizontals  of  this  plane;  they  also 
lie  respectively  in  the  planes  of  the  horizontal  curves  (9,0), 


22  SYSTEM    OF    FORTIFICATIOX    DRAWIXG. 

(8,0),  etc. ;  but,  since  thej  fall  exterior  to  the  curves,  it  fol- 
lows tliat  their  plane  also  lies  exterior  to  every  horizontal 
curve  of  the  surface,  except  at  the  curve  (10,0)  where  it 
touches  the  surface  at  the  point  of  contact  of  its  horizontal 
(10,0)  with  this  curve. 

2d.  When  the  line  a  b,  PL  1,  Fig.  IT,  is  horizontal,  let 
tangents  be  drawn  to  the  horizontal  curves  and  parallel  to 
a  h.  These  tangents  may  be  regarded  as  the  elements  of  a 
cylinder  which  envelops  the  surface,  the  tangent  plane  to 
which  will  be  tangent  to  the  surface.  To  find  the  element 
of  contact  of  the  plane  and  cylinder,  let  the  cylinder  and 
given  line  be  intersected  by  an  arbitrary  vertical  plane,  of 
which  0  d  is  the  trace.  From  the  point  o,  where  the  line 
pierces  this  plane,  let  a  tangent  line  be  drawn  to  the  curve 
cut  from  the  cylinder  by  the  plane,  by  Prob.  10.  The 
point  of  contact  will  determine  the  position  of  the  element 
of  the  cylinder  along  which  the  plane,  through  a  b,  will  be 
tangent:  since  the  tangent  to  the  curve  projected  in  od, 
with  the  line  a  b,  will  determine  the  tangent  plane  to  the 
cylinder. 

3d.  When  the  line  a  b,  PI.  1,  Fig.  18,  is  so  nearly  hori- 
zontal that  tangents  cannot  be  drawn  from  its  points,  with- 
in the  limits  of  the  drawing,  to  the  horizontal  curves,  let 
au}^  point  of  the  line,  as  o  (7,0),  be  taken  as  the  vertex  of  a 
cone  enveloping  the  surface ;  a  plane  passed  through  the 
line  and  tangent  to  the  cone  will  be  tangent  to  the  surface. 

Find,  by  Probs.  10  and  11,  the  curve  m  r  n  cut  from  this 
cone  by  the  horizontal  plane  (8,0);  from  the  point  (8,0)  of 
a  b  draw  a  tangent  to  this  curve.  This  tangent,  with  the 
line  (I  b,  will  determine  the  required  plane. 

33... Prob.  15,  Pl.  1,  Fig.  19.  To  find,  cq^proximatehj,  the 
'point  where  a  given  right  line  jnerces  a  surface. 

Let  (8,0),  (9,0),  etc.,  be  the  horizontals  of  the  surface, 
and  dftliQ  scale  of  declivity  of  the  line.  Through  any  two 
points,  as  a  (9,0)  and  c  (8,0),  draw  two  parallel  lines,  as 
am  and  en,  which  may  be  taken  as  the  horizontals  of  an 
arbitrary  plane  passed  through  the  given  line.  Joining  the 
points  m  n  where  the  horizontals  of  the  arbitrary  plane 


SYSTEM    OF    FORTIFICATION    DRAWING.  23 

intersect  the  coiTesponding  horizontals  of  the  surface,  this 
line  m  ?i  will  be  the  approximate  intersection  of  the  plane 
with  the  zone  of  the  surface  between  the  horizontals  (8,0) 
and  (9,0),  and  the  point  o,  where  m  n  intersects  <//,  will  be 
the  approximate  point  required. 

34...PR0B.  16,  Pl.  1,  Fig.  20.  To  find  the  intersection  of  a 
2)lane  and  surface. 

Let  (10,0),  (9,0),  etc.,  be  the  horizontal  curves  of  tlie  sur- 
face, cf  the  scale  of  declivity  of  the  plane. 

Draw  the  horizontals  of  the  plane  having  the  same  refer- 
ences as  the  horizontal  curves ;  the  points  of  intersection 
of  these  lines,  in  their  respective  planes,  will  be  points  of 
the  required  intersection. 

When  it  is  desired  to  tind  a  point  of  the  curve  of  inter- 
section intermediate  to  two  horizontal  curves,  if  the  refer- 
ence of  the  required  point  is  fixed,  it  will  be  necessary  to 
construct,  Art.  27,  the  horizontal  curve  of  the  surfoce,  and 
the  horizontal  of  the  plane  having  this  reference  ;  their  in- 
tersection will  give  the  required  point.  If  the  reference  of 
the  required  point  is  not  fixed,  draw  any  generatrix,  as  ac^ 
of  the  zone  on  which  the  required  point  is  to  be  found,  and, 
by  Prob.  8,  Fig.  11,  find  the  point,  as  o,  where  a  c  pierces 
the  given  plane ;  this  will  be  the  required  point. 

35... Application  of  Preceding  Problems.  The  follow- 
ing problems  will  aid  as  illustrations  of  the  preceding  sub- 
ject in  its  application  to  the  determination  and  delinea- 
tion of  lines  and  surfaces. 

36... Prob.  1,  Pl.  2,  Fig.  2.  The  plane  of  site  of  a  work, 
the  exterior  line  and  scale  of  declivity  of  its  terreplein  being 
given,  to  construct  the  i^lane  of  the  rampart-slope  and  its  foot; 
also,  a  ramp  of  a  given  inclination  along  the  rampart-slope,  lead- 
ing from  the  plane  of  site  to  the  terreplein. 

Let  a  (74,50)  and  b  (76,0)  be  the  references  of  two  })oints 
on  the  exterior  line  of  the  terreplein,  and  ui  n  its  scale  of 
declivity ;  let  the  rami)art-sloi>e  be  ^  ;  the  declivity  of  the 
ramp  J,  its  width  4.30  yards;  and  the  plane  of  site  be  hori- 
zontal and  at  the  reference  (60,0). 

The  foot  of  the  ranipart-slope  lying  in  the  plane  of  site 


24  SYSTEM    OF   FORTIFICATION    DRAWING. 

will  be  horizontal,  and  will  be  determined,  Prob.  6,  Fig.  8, 
by  finding  the  line  of  the  slope  at  the  reference  (60,0). 

Having  the  two  bounding  lines  of  the  rampart-slope,  the 
inner  line,  cd^  of  the  ramp  is  constructed  by  assuming  a 
point,  c,  on  the  foot  of  the  rampart-slope,  as  the  point  of 
departure,  and  determining  the  line  of  ^,  drawn  from  c,  on 
the  rampart-slope,  by  Prob.  3,  Fig.  5.  Having  found  this 
line,  which  is  also  the  line  of  greatest  declivity  of  the  ramp, 
the  exterior  line,  c/,  of  the  ramp  is  drawn  parallel  to  it,  and 
at  a  distance  4.30  yards,  equal  to  the  width  assumed  for  the 
ramp.  The  horizontals  of  the  ramp  will  be  perpendicular 
to  these  two  lines.  The  foot  of  the  ramp,  c  e,  will  be  a  hori- 
zontal line  drawn  through  the  point  of  departure.  The 
top  of  it,  (If,  will  be  determined,  b}-  Prob.  7,  Fig.  9,  by  find- 
ing the  intersection  of  the  ramp  and  the  terreplein,  one 
point  of  which  will  be  the  point  d  (76,30),  the  intersection 
of  the  inner  line  of  the  ramp  and  the  interior  line  of  the 
terreplein. 

The  ramp  is  terminated  on  the  exterior  by  passing  a 
plane  through  its  exterior  line  ef,  having  the  same  slope  as 
the  rampart-slope.  This  plane  will  intersect  the  plane  of 
site  in  a  line  parallel  to  the  foot  of  the  rampart-slope,  and, 
the  terreplein  in  one  parallel  to  the  exterior  line  of  the 
terreplein. 

37... Prob.  18,  Pl.  2,  Fig.  3.  Having  given  the  lines  of  the 
'parapet  of  a  work,  and  the  scales  of  declivity  of  the  jolanes  of  its 
interior  crest  and  terrej^lein,  to  determine  the  lines  and.  surfaces  of 
a  barbette  in  its  salient  for  five  guns. 

Let  a  6  be  the  scale  of  declivity  of  the  plane  of  the  inte- 
rior crest,  which,  as  the  terreplein  is  parallel  to  the  plane  of 
the  interior  crest  and  8  feet  below  it,  estimated  vertically, 
will  also  serve  as  the  scale  of  declivity  of  the  terreplein,  by 
subtracting  8  feet  from  the  references  of  the  former  to 
obtain  the  corresponding  references  of  the  latter.  Having 
constructed  a  pancoupe  of  4  yards  in  the  salient,  find  the 
intersection  of  the  top  surface  of  the  barbette,  which  is 
horizontal  and  assumed  on  the  drawing  at  the  reference 
(82,75),  with  the  planes  of  the  interior  slope,  this  intersec- 


SYSTEM    OF    FORTIFICATION    DRAWING.  20 

tion  will  deterniiiie  the  foot  of  the  genouillere  of  the  bar- 
bette. From  tills  last  line  at  the  paiicoupe  set  back  aloni:^ 
the  capital  a  distance  of  8  yards,  and  from  the  extremity  of 
this  line  draw  a  perpendicular  to  the  interior  crest  of  each 
face.  The  pentagonal  iigure  thus  marked  out  will  be  the 
space  for  the  gun  in  the  salient.  From  the  foot  of  each  of 
the  perpendiculars  set  oft'  along  the  faces  distances  of  12 
yards,  for  the  lengths  along  the  interior  crests  to  be  occu- 
pied by  two  guns  on  each  side  of  the  salient.  Setting  back 
from  the  extremities  of  these  two  last  distances,  set  oft'  per- 
pendiculars to  the  interior  crest  of  8  yards,  and  drawing 
lines  through  the  extremities  of  these  perpendiculars  paral- 
lel to  the  interior  crests,  the}-,  with  the  two  perpendiculars, 
will  mark  out  the  exterior  bounding  lines  of  the  barbette. 
By  passing  planes  of  |  or  4.5°  through  these  exterior  lines, 
and  finding,  by  Prob.  7,  Fig.  9,  their  intersections  with  the 
terreplein,  these  lines  will  be  the  foot  of  the  barbette-slopes. 
A  ramp,  having  a  slope  J,  leads  from  the  terreplein  to  the 
toj!  of  the  barbette  ;  the  width  of  this  ramp  is  3.30  ya'ds, 
its  interior  line  in  projection  being  on  the  prolongation  of 
the  foot  of  the  banquette-slope.  The  ramp  is  terminated 
by  side-slopes  of  {,  the  intersections  of  which  with  the  ter- 
replein and  the  slopes  of  the  barbette  and  banquette  are 
found  by  Prob.  7,  Fig.  9.  The  foot  of  the  ramp,  or  its 
intersection  Avith  the  terreplein,  is  also  found  by  the  same 
problem. 

As  the  top  surface  of  the  barbette  is  horizontal,  it  may 
1)0  necessary  in  some  cases  to  make  the  interior  crest,  along 
the  barbette,  also  horizontal,  in  which  case  the  su})crior 
slope  of  the  parapet  along  the  barbette  being  higher  than 
the  rest  of  it,  the  two  planes  will  be  connected  by  a  plane 
of  45°,  as  at  c. 

38... Prob.  10,  Pl.  2,  Fig.  4.  To  ddennine  (he  bounding 
surfaces  of  a  ramj)  leading  up  an  irregular  surface,^  and  so  placed 
thai  its  axis  or  centre  line  shall  nearly  coincide  with  the  irregular 
surface. 

Let  (8,0),  (9,0),  etc.,  be  the  horizontal  curves  of  the  sur- 
face, and  let  (/  (8,0)  be  the  point  of  departure  or  foot  of  tlie 


26  SYSTEM    or    FORTIFICATION    DRAWING. 

ramp.  Assuming  the  declivity  of  the  ramp  i,  for  example, 
from  (7.,  with  a  radius  of  9  units,  describe  an  arc,  and  join 
by  a  right  line  the  point  b  where  it  cuts  the  horizontal  (9,0) 
with  the  point.  Repeat  this  construction,  from  b  to  c,  on 
the  horizontal  (10,0) ;  and  so  on  to  the  top,  e,  or  point  of 
arrival.  The  broken  line  a-b-c-d-e  will  be  the  projection  of 
the  axis.  But,  to  avoid  the  angular  changes  of  direction, 
the  straight  portions  of  the  axis  may  be  connected  at  the 
angular  points,  by  setting  oft*  from  6,  for  example,  the  equal 
distances  b  a',  b  c',  and  connecting  these  points  by  an  arc  of 
a  circle  tangent  to  the  straight  portions.  The  same  con- 
struction being  repeated  at  the  other  angular  points,  the 
broken  line  will  be  replaced  by  the  sinuous  line  a  a'  c',  etc., 
as  the  axis.  Having  determined  the  axis,  the  exterior  and 
interior  lines  of  the  top  surface  are  drawn  parallel  to  the 
axis,  and  at  a  distance  from  it  equally  to  half  the  assumed 
wndth  of  the  ramp.  From  the  position  of  the  axis,  the 
exterior  half  of  the  ramp  will  be  in  embankment,  and  the 
interior  in  excavation.  To  determine  the  side-slopes  of 
the  embankment,  pass  planes  through  the  straight  portions 
of  the  exterior  edge  of  the  ramp,  and  find,  by  Prob.  6, 
PI.  1,  Fig.  8,  the  horizontals  of  these  planes,  and,  by  Prob. 
16,  Fig.  20,  the  intersections  of  these  planes  with  the  irre- 
gular surface.  The  plane  surfaces  of  the  side-slopes  thus 
determined,  are  connected  by  curved  surfaces  which  pass 
through  the  curved  lines  of  the  exterior  edge.  These  sur- 
faces ma}^  be  determined  as  follows  :  Take,  for  example, 
the  point  n  at  the  foot  of  the  plane  side-slope  A,  where  it 
cuts  the  radius  prolonged,  of  the  arc  a'  c' ;  and  the  point  0 
on  the  radius  through  c'  where  it  cuts  the  foot  of  the  plane 
side-slope  B.  The  lines,  of  which  nv  and  ou  are  the  pro- 
jections, will  evidently  have  the  same  inclination,  and  they 
may  be  assumed  as  the  lines  of  junction  of  the  plane-slopes 
A  and  B  and  the  curved  side-slope  x.  This  curved  side- 
slope  may  then  be  generated  by  the  motion  of  a  right  line, 
which  has  the  top  line  of  which  v  u  is  the  projection  for  its 
directrix,  whilst  in  its  motion  it  makes  a  constant  angle 
Avith  the  plane  of  comparison,  and  its  projections  are  con- 


SYSTEM    OF    FORTIFICATION    DRAWING.  27 

stantly  normal  to  the  arc  v  u .  From  the  construction  com- 
prising these  conditions,  the  foot,  ??  o,  of  the  curved  portion, 
X,  of  the  side-slope  is  determined.  The  same  constructions 
are  repeated  to  obtain  the  portions,  C,  of  the  plane,  and  y  ^ 
of  the  curved  side-slopes,  with  the  line  m-n-o-p-q-r-s  the  foot 
of  these  slopes. 

The  side-slopes  of  the  part  in  excavation  A',  B',  O  and 
x' y'  with  the  line  m' -n' -o' -f -q' -r' ,  are  determined  by  like 
constructions. 

The  portions  of  the  top  surfaces  of  the  ramps,  bounded 
by  the  arcs  of  circles,  are  helicoidal  surfaces,  of  which  the 
axis  is  the  directrix  and  the  plane  of  comparison  the  plane 
director. 

The  curved  surface  side-slopes  are  also  evidently  heli- 
coidal surfaces,  the  directrices  of  which  are  the  curved 
lines  above  mentioned;  and  the  vertical  lines  through  the 
centres  of  the  arcs  the  projections  of  these  lines. 

Remarks.  In  the  Figure,  the  declivity  of  the  side-slopes 
of  the  embankment  is  one-half  the  excavation.  The  decliv- 
ities of  the  curved  portions  of  the  top  are  greater  than 
those  of  plane  surfaces,  the  difference  depending  on  the 
angle  between  the  straight  portions  of  the  axis. 

S9...PIan,  Section,  Elevation  and  Profle. 

In  delineating  permanent  fortifications,  horizontal  pro- 
jections and  horizontal  sections,  both  of  which  go  under  the 
general  name  of  jilans,  are  used  to  represent  the  relative 
positions  of  the  parts  and  their  dimensions  horizontally. 
Intersections  of  the  parts  by  vertical  planes  passed  in  any 
required  direction,  and  termed  sections,  show  the  relative 
positions  and  dimensions  of  all  the  parts  in  the  plane  of 
section,  both  horizontally  and  vertically.  Projections  on  a 
vertical  plane,  termed  elevations,  are  used  to  represent  the 
forms  of  the  exterior  surfaces  of  the  parts  projected  and 
their  relative  positions  vertically.  Profiles  are  sections 
made  by  vertical  planes  passed  perpendicular  to  the  hori- 
zontal projections  of  the  interior  crests  of  the  parts  where 
the  profiles  are  taken ;  they  give  the  vertical  and  horizontal 


28  SYSTEM    OF   FORTIFICATION   DRAWING. 

distances  between  the  points  in  the  plane  of  the  profile. 
Usually,  a  profile  only  shows  the  bounding  lines  of  the  parts 
intersected,  thus  presenting  nothing  more  than  an  outline 
of  the  parts. 

In  giving  a  horizontal  section,  it  is  customarj^iot  only  to 
delineate  the  forms  contained  in  the  plane  of  section,  but  to 
project  upon  this  plane  all  the  parts  which  are  seen  bdoiv  it, 
and  in  some  cases  parts  which  are  covered  by  others,  the 
outlines  of  the  latter  being  shown  by  broken,  or  dotted, 
lines,  to  distinguish  them  from  the  outlines  of  the  parts  in 
view,  for  wdiich  full  lines  are  used.  A  like  method  is 
sometimes  employed  in  sections,  the  visible  parts  beyond 
the  plane  of  section  being  projected  upon  it;  thus  combin- 
ing an  elevation  and  section  in  the  same  figure. 

For  the  perfect  comprehension  of  a  fortification,  not  only 
will  all  of  the  foregoing  modes  of  delineation  be  requisite, 
but  the  references  of  all  the  points  and  lines,  as  well  as 
the  vertical  and  horizontal  distances  that  determine  the 
relative  positions  of  the  points,  must  be  carefully  written 
on  each  figure. 

In  PI.  3,  Figs.  1,  2, '3,  which  show  the  plan,  section  and 
elevation  of  the  end  of  the  face  of  a  w^ork,  an  illustration 
is  given  of  the  usual  manlier  in  which  such  drawings  are 
made ;  and  the  same  system  wdll  be  pursued  in  the  figures 
which  follow  these. 

40... Observations  on  the  means  for  obtaining  accuracy  in 
drawings. 

The  first  requisite  in  all  drawings  intended  to  represent 
not  only  the  outline  of  the  forms  of  objects,  but  to  afford 
the  means  of  determining  the  exact  dimensions  of  each 
part,  is  minute  accuracy,  both  in  the  geometrical  construc- 
tions, and  in  wa-iting  down  all  letters  and  numbers  which 
serve  either  as  references  or  to  give  the  dimensions. 

To  attain  this  end,  so  far  as  regards  the  geometrical  part, 
judgment  is  to  be  exercised  in  the  selection  of  the  means 
for  establishing  on  the  drawing  the  positions  of  the  various 
points  which  are  either  given  or  to  be  found;  as  one 
method,  although  in  theory  as  correct  as  some  other,  may 


SYSTEM    OF   FORTIFICATION    DRAAVING.  29 

not,  ill  practice,  be  found  to  yield  as  satisfactory  results. 
Attention  to  the  following  remarks  will  serve  both  to  illus- 
trate the  meaning  here  intended,  and  to  give  some  simple 
practical  methods  : 

1st.  In  setting  off  several  distances  along  a  line,  whether 
equal  or  unequal,  the  most  accurate  method  is  to  commence 
by  first  setting  off  the  entire  distance,  and  then  the  several 
parts;  taking  care  to  verify,  from  the  scale,  the  aggregate 
of  the  several  partial  distances;  thus,  in  the  annexed  PI.  2, 
Fig.  5,  where  the  aggregate  of  all  the  partial  distances  is 
60.33  feet,  commence  by  setting  off  the  entire  distance 
60'.33  feet;  next  50'.33,  which  is  the  sum  of  the  two  dis- 
tances, 20'  and  30'. 33,  then  verify  the  remaining  10'  by  the 
scale. 

2d.  When  a  distance  to  be  set  off  is  so  small  that  it 
cannot  be  laid  down  with  accuracy  by  the  points  of  the 
dividers,  the  following  metht)d  may  be  employed:  set 
back,  from  the  point  from  which  the  required  distance  is 
to.  be  set  off,  any  arbitrary  distance,  then  set  forward,  from 
this  last  point,  a  distance  equal  to  the  sum  of  this  arbitrary 
distance  and  the  one  required;  thus,  in  PI.  2,  Fig.  6,  where 
2'  is  to  be  set  off  from  a  toward  r,  set  back  from  a  say  30' 
to  6,  then  from  h  32'  to  c. 

3d.  In  setting  off  a  point  at  a  given  perpendicular  dis- 
tance from  a  line,  instead  of  drawing  a  perpendicular,  in 
the  iirst  place,  to  the  line,  it  will  mostly  be  found  more 
speedy,  and  more  accurate,  to  take  off  from  the  scale  the 
given  distance,  in  the  dividers,  and,  setting  one  point  on 
the  paper,  bring  the  other  so  that  the  arc  described  by  it, 
with  the  given  distance  as  a  radius,  shall  be  tangent  to  the 
line;  thus,  in  PI.  2,  Fig.  7,  Avishing  to  set  off  c  at  20'  from 
a  6,  take  20'  in  the  dividers,  and,  by  the  eye,  find  where  one 
point  must  be  placed  so  that  the  other  describing  an  arc 
will  touch  ah.  This  method  will  be  found  convenient  in 
drawing  a  parallel  to  a  line  at  a  given  distance  from  it  by 
setting  off  another  point  in  the  same  way. 

4th.  In  setting  off  several  points,  for  the  purpose  of  draw- 
ing several  parallels  to  a  given  line,   as,  for  example,  the 


30  SYSTEM    OF   FORTIFICATION   DRAWING. 

lines  wliicli  bound  the  planes  of  a  parapet,  it  will  be  found 
most  speedy  and  accurate  to  draw  upon  a  slip  of  smooth 
thin  paper  two  lines  perpendicular  to  each  other;  mark  on 
one  of  the  lines  the  respective  given  distances  from  the 
other;  then  cut  the  paper  close  to  the  line  along  which  the 
given  points  are  marked  otf;  so  that,  when  the  strip  is  laid 
upon  the  drawing,  the  other  line  marked  upon  it  being  laid 
upon  the  line  of  the  drawing  to  which  the  parallels  are  to 
be  drawn  can  be  pricked  off,  either  b}"  a  sharp-pointed  pen- 
cil, or  in  any  other  way.  In  PI.  2,  Fig.  8,  ab  is  the  line  of 
drawing;  A  the  strip  of  paper, /c,/<:/,/(3,  etc.,  the  distances 
at  which  the  parallels  are  to  be  drawn  from  a  b,  marked  ofl' 
on  the  edge  of  A  perpendicular  to  the  line  /,  which  line, 
when  J.  is  laid  on  the  drawing,  should  coincide  with  a  5. 
If  the  line  a  6  is  somewhat  long,  it  will  be  better  to  set  ofi' 
these  points  near  each  of  its  extremities  than  to  draw  the 
parallels  by  aid  of  the  ruler  and  triangle. 

5th.  When  a  point  is  to  be  constructed  by  means  of  the 
intersection  of  two  lines  arbitrarily  chosen,  such  a  position 
should  be  assumed  for  the  arbitrary  lines  that  they  shall  not 
form  a  very  acute  angle,  as  in  that  case  their  point  of  inter- 
section might  not  be  determined  by  the  eye  with  accuracy. 
For  example,  in  erecting  a  perpendicular  to  a  line  at  a  given 
point,  and  in  like  problems,  in  which  points  are  found  by 
the  intersections  of  arcs  of  circles,  it  will  be  usually  most 
convenient,  and  best,  to  take  for  the  radii  of  the  arcs  the 
distance  between  their  centres,  as  the  angle  between  the 
tangents  to  the  arcs  at  their  point  of  intersection  will  then 
be  60°,  which  is  sufficient  to  give  accuratelj'  the  point 
where  the  lines  cross.  In  cases  like  Figs.  10,  11,  Arts.  22, 
23,  the  arbitrary  lines  ab,  a'  b',  etc.,  should  be  so  chosen  as 
to  intersect  the  horizontals  nearly  at  right  angles,  and  so, 
also,  that  the  resulting  lines,  by  which  the  points  o,  o'  are 
determined,  shall  not  intersect  in  too  acute  an  angle. 

In  all  such  cases  of  determining  points,  and  even  where 
a  point  is  pricked  into  the  paper  by  a  sharp  point,  it  will 
be  found  well  to  mark  the  point  thus  o,  by  a  small  circle 
drawn  around  it  with  the  lead  pencil,  as  this  will  present 
the  point  with  more  distinctness. 


SYSTEM    OF    FORTIFICATIOX    DRAWING.  31 

6tb.  In  determining  a  portion  of  a  line,  bj  the  eonstnic- 
tion  of  two  arbitrary  points,  the  points  should  be  so  chosen 
that  the  portion  required  may  fall  between  them  and  not 
beyond  them.  In  PI.  1,  Fig.  10,  for  example,  if  the  required 
portion  of  the  line  of  intersection  of  the  planes  extended 
on  either  side,  beyond  o,  or  o',  or  beyond  both,  the  lines  a  h, 
c  d,  etc.,  should  be  so  chosen  as  to  bring  o  and  o'  as  far 
apart,  at  least,  as  the  length  of  the  required  portion  of  the 
line  which  they  serve  to  determine. 

7th.  No  means  of  verifying  the  accuracy  of  the  con- 
struction of  points,  or  lines,  should  be  omitted.  In  PI.  1, 
Fig.  9,  for  example,  other  corresponding  horizontals  should 
be  drawn,  and  if  the  line  of  intersection  determined  by  the 
two  points  first  found  is  correct,  their  points  of  intersection 
also  will  fall  upon  it.  In  PL  1,  Figs.  9,  10,  the  scale  of  de- 
clivity of  the  line  of  intersection  being  determined,  the 
references  of  the  points,  where  it  intersects  the  scales  of 
declivity  of  the  planes,  should  be  the  same  as  the  same 
points  on  the  scales,  if  the  line  has  been  accurately  deter- 
mined. A  general  and  minute  verification  of  all  the  parts 
of  the  drawing  should  be  made  before  any  portion  of  it  is 
put  in  ink. 

8th.  Xeatness  is  a  not  unimportant  element  in  the  at- 
tainment of  accuracy  in  drawing.  A  few  minutiae,  when 
attended  to,  will  subserve  this  end. 

That  part  of  the  paper  on  which  the  draughtsman  is  not 
working  should  be  kept  covered  with  clean  paper,  pasted 
on  the  edge  of  the  board  so  as  to  fold  over  the  drawing; 
the  parts  which  are  finished  should  be  similarly  protected. 

Before  commencing  the  dail}'  work  the  paper  should  be 
carefully  dusted,  and  the  scales,  rules  and  triangles  be  care- 
fully wiped  with  a  clean  dry  rag. 

As  few  lines  of  construction  as  possible  should  be  drawn 
in  pencil;  and  only  that  part  of  each  which  may  be  strictly 
necessary  to  determine  the  point  sought.  As,  for  example, 
where  a  point  is  to  be  found  by  the  intersection  of  two  arcs 
of  circles;  when  the  position  of  the  point  can  be  approxi- 
mately judged  of  by  the  eye,  only  a  portion  of  one  arc, 


32  SYSTEM    OF   FORTIFICATIOX    DRAWING. 

wlilcli  will  embrace  the  point,  may  be  drawn,  and  the  point 
where  the  second  arc  would  intersect  the  first  be  marked 
without  describing  the  arc.  In  PI.  1,  Fig.  10,  instead  of 
drawing  the  entire  lines  a  6,  c  d,  etc.,  it  would  be  simply 
necessary  to  mark  the  points  only  where  they  cut  the  hori- 
zontals, and,  in  like  manner,  the  points  o  and  o'  might  be 
marked  without  drawing  the  entire  lines. 

ISTo  more  of  any  line  of  the  drawing  should  be  made  in 
pencil  than  what  is  to  remain  permanently  in  ink. 

9th.  In  inking  the  lines,  the  following  directions  will  be 
found  useful : 

Efface  carefully  all  pencil  lines  that  are  not  to  be  inked, 
and  those  parts  of  the  permanent  lines  which  are  not  to 
remain,  before  commencing  to  ink. 

When  right  lines  are  tangent  to  curves,  put  in  ink  the 
curve  before  the  right  line  ;  draw  all  arcs  of  equal  radii  at 
once,  one  after  the  other;  if  several  arcs  are  to  be  described 
from  the  same  centre,  it  will  be  well  to  put  a  thin  bit  of 
quill  over  the  point  for  the  end  of  the  dividers  to  rest  on, 
to  avoid  making  a  large  hole  in  the  drawing. 

If  the  drawing  is  not  to  be  colored  with  the  brush,  all 
the  lines  of  one  color  should  be  put  in  before  commencing 
on  those  of  another. 

If  one  of  the  bounding  lines  of  a  surface  is  to  be  made 
heavier  than  the  others,  its  breadth  should  be  taken  from 
the  surface  they  limit  and  not  be  added  to  it;  and  when 
the  heavy  line  forms  the  boundary  of  two  surfaces,  its 
breadth  must  be  taken  from  the  one  of  greatest  declivity. 

10th.  "When  the  drawing  is  to  be  colored,  all  lines  that 
are  not  to  be  black  may  be  put  in  first  with  black — making 
them  ver}^  faint,  so  that  they  may  receive  their  appropriate 
colors  after  the  drawing  is  otherwise  completed. 

No  heavy  line  should  be  put  in  until  the  work  with  the 
brush  is  completed. 

When  all  the  lines  are  in,  the  drawing  should  be  thor- 
oughly cleaned  with  stale  bread-crumb ;  and  then  have 
several  pitchers  of  water  dashed  over  it,  the  board  being 
placed  in  an  inclined  position  to  allow  the  water,  colored 


SYSTEM    OF   FORTIFICATION    DRAAVING.  33 

by  the  ink  lines,  to  escape  rapidl}'-,  and  not  to  discolor  tlie 
paper. 

lltb.  In  nsing  the  brush,  whether  for  flat  tints,  or 
graded,  the  requisite  depth  of  tint  should  be  reached  by  a 
number  of  faint  tints  laid  over  each  other;  this  is  especially 
necessary  in  laying  tints  of  blacks,  browns  and  reds. 

To  obtain  an  even  flat,  or  graded  tint,  on  dry  paper,  is 
very  difficult  for  a  beginner.  The  best  plan  for  this  is, 
first  to  wet  with  a  large  brush,  or  clean  rag,  the  surface  on 
which  the  tint  is  to  be  laid,  then,  with  a  slightly  moist  rag, 
clear  the  surface  of  water,  and  before  the  paper  has  time  to 
dry  lay  on  the  tint.  With  this  precaution,  the  heaviest 
tints  of  Chinese  ink,  the  most  difticult  of  all  to  manage  on 
dry  paper,  can  be  neatly  laid  down. 

12th.  The  lettering  and  numbering  of  a  drawing  should 
be  in  ordinary  printed  character;  this  is  particularly  requi- 
site in  the  numbering,  to  avoid  misapprehensions  which 
might  arise  from  individual  peculiarities  in  writing  num- 
bers. 

As  has  been  already  remarked,  references  are  written  in 
black,  within  brackets,  which,  when  practicable,  embrace 
the  point  referred  to.  "When  not  practicable,  a  small 
dotted  line  may  lead  from  the  point  to  the  reference ;  thus, 

o (25,50);    but   to    distinguish    references    from    other 

numbers  the  designation  of  the  unit  is  omitted. 

All  horizontal  distances  between  points  are  written  upon 
a  dotted  line  drawn  between  the  points,  with  an  arrow 
head  at  each  end;  where  several  jiartial  distances  in  a  right 
line  are  marked,  it  will  be  also  well  to  mark  the  total  dis- 
tance—  the  latter  may  be  written  above  or  beneath  the 
former,  PI.  2,  Fig.  5. 

In  writing  horizontal  distances,  the  usual  designation  of 
the  unit  is  always  written  thus:  y,  for  yards,  '  for  feet,  etc. 
All  the  numbers  must  be  expressed  in  the  same  unit;  the 
fractional  parts  being  in  decimals. 

References  and  horizontal  distances  cannot  be  too  much 
multiplied,  in  order  to  avoid  misapprehensions,  and  the 
results  of  errors  of  construction,  as  well  as  to  save  the 
3 


34  SYSTEM    OF    FORTIFICATION    DRAWING. 

time  tliat  would  be  taken  in  applying  dividers  to  the  draw- 
ing to  find,  from  the  scale  affixed  to  it,  the  dimensions  of 
any  part. 

A  scale  very  accurately  constructed  should  be  affixed  to 
the  drawing  before  it  is  cut  from  the  board  ;  so  that  the 
jihi'inkage  of  the  paper,  which  is  about  ^-J^,  may  affect  all 
the  parts  equally,  and  the  scale  thus  be  made  to  correspond 
to  the  real  lengths  of  the  lines  on  the  drawing.  The  scale 
should  be  divided  according  to  the  decimal  system,  as 
being  most  convenient  for  counting  off. 

The  first  division  of  the  scale  should  furnish  the  units, 
and  also  their  decimal  parts,  if  the  scale  bears  that  propor- 
tion to  the  true  dimensions  of  the  object  represented  which 
will  admit  of  these  divisions.  This  first  division  is  num- 
bered from  right  to  left,  PI.  2,  Fig.  9,  the  zero  point  being 
on  the  right,  the  10  point  on  the  left;  the  succeeding  divis- 
ions, to  50  inclusive,  should  each  be  equal  to  the  first  di- 
vision, containing  ten  units  each.  The  remaining  divis- 
ions may  contain  fift}'  units  each.  It  will  be  seen  that  any 
number  of  tens,  units,  or  fractional  parts  of  a  unit,  can 
thus  be  readily  taken  off  from  the  scale  by  the  dividers. 
The  scale  should  be  long  enough  to  give  the  dimensions  of 
the  longest  line  on  the  drawing. 

The  proportion  which  the  scale  bears  to  the  true  dimen- 
sions of  the  object  should  be  written  above  the  scale ;  thus, 
S'Hile  one  inch  to  ten  yards,  or  ^l^.  And  the  designation  of 
the  unit  of  the  drawing  should  be  annexed  to  the  last 
division  on  the  scale,  as  yds.  for  yards,//,  for  feet,  etc. 


PERMANENT  FORTIFICATION. 


flrdiminarii  (3|oiifii(li>ratioiis, 


41... The  term  permanent  fortification  is  applied  to  those 
defences  -which,  constructed  of  materials  of  a  durable  ua- 
ture,  and  designed  for  permanent  occupancy  by  troops, 
receive  such  a  degree  of  strength  that  an  enemy  will  he 
forced  to  the  operations  either  of  a  siege  or  a  blockade  to 
gain  possession  of  them. 

42... The  object  of  such  defences  is  to  secure  the  per- 
manent military  possession  'of  those  points,  either  on  the 
frontiers  or  in  the  interior  of  a  state,  -which  must,  at  all 
times,  have  a  well-detined  bearing  on  the  operations  of  a 
defensive  or  an  oflensivc  Avar. 

43. ..For  the  attainment  of  this  object,  the  folio-wing  gen- 
eral conditions  should  be  fulfilled  in  the  arrangement  of 
such  defences :  1st,  they  should  be  of  sufficient  strength  to 
resist  with  success  all  the  ordinary  means  resorted  to  hy  an 
assailant  in  an  open  assault ;  2d,  be  provided  with  suitable 
shelters  to  protect  the  troops,  the  armament,  and  the  mag- 
azines of  provisions  and  munitions  of  war  required  for 
their  defence,  against  the  destructive  measures  of  the  as- 
sailant, of  every  description  ;  3d,  be  so  planned  that  every 
point  exterior  to  the  defences  within  cannon  range  shall  be 
thoroughly  swept  by  their  fire ;  4th,  have  secure  and  easy 


f 

36  COMPONENT    ELEMENTS    OF    PERMANENT    WORKS. 

means  of  communication  for  tlie  movements  of  the  troops, 
both  Avithin  tlie  defences  and  to  the  exterior;  oth,  and 
finally,  be  provided  with  all  such  accessory  defensive  means 
as  the  natural  features  of  the  position  itself  may  atford,  to 
enable  the  garrison  to  dispute  with  energy  the  occupancy 
by  the  assailant,  of  every  point  both  within  and  exterior  to 
the  defences. 

The  defensive  branch  of  the  military'  engineer's  art  con- 
si^^ts  in  a  knowledge  of  the  means  which  are  employed  to 
fulfil  the  above  conditions,  and  of  their  suitable  ada[)tation 
to  the  natural  features  of  the  positions  he  may  be  called 
upon  to  fortify. 


(l^omponcuf  ([;lcnicntf)  of  pcnnanrnt  Mlorlifi. 


GENERAL  PROFILE. 

44. ..The  first  condition  laid  down  for  permanent  de- 
fences, security  from  open  assault,  supposes  a  strength  of 
profile  greatly  superior  to  that  which  is  given  to  temporary 
works. 

45... The  usual  and  most  simple  form  of  profile  for  per- 
manent works  consist  of  a  rampart^  a  parapet,  and  a  ditch, 
the  scarp  and  counterscarp  of  which  are  fiiced  with  steep 
walls  of  stone,  or  brick,  and  exterior  to  which  a  glacis  is 
usually  thrown  up.  When  the  ditch  contains  at  all  times 
a  dcj)th  of  water  sufficient  to  prevent  its  being  forded,  the 
scarp  and  counterscarp  may  be  simply  slopes  of  earth  like 
those  of  field  works;  as  the  water,  with  ordiiuiry  vigilance 
on  the  part  of  tlie  defence,  will  give  security  from  surprise, 
and  all  the  other  ordinary  means  of  an  open  assault. 

46. ..The  rampart,  A,  PI.  3,  Figs.  4,  6,  is  an  earthen 
mound,  raised  above  the  natural  level  of  the  ground,  and 


COMPONENT   ELEMENTS   OF    PERMANENT    WORKS.  37 

upon  which  the  parapet,  -C,  is  placed.  The  rampart  thus 
serves  to  give  the  troops  and  arnianent,  which  are  placed 
on  top  of  it  and  behind  the  parapet,  a  commanding  view 
over  the  ground  to  be  guarded  by  the  fire  of  the  defences  ; 
whilst,  at  the  same  time,  it  inei-eases  the  obstacle  to  an 
open  assault,  by  the  additional  height  it  gives  to  the  scarp. 

47. ..The  top  surface  of  the  rampart,  6  c,  in  rear  of  the 
parapet,  termed  the  tcrrcplcin^  affords  the  troops  and  arma- 
ment a  convcuicnt  position  for  circulation  from  point  to 
point,  where  they  are  sheltered  from  the  direct  views  of 
the  assailant's  fire. 

48... The  rampart  is  usually  terminated  on  the  interior, 
ah,  by  allowing  the  earth  to  assume  either  its  natural  slope 
or  one  somewhat  less  steep,  and  which  is  termed  the  ram- 
paj't-slope.  In  cases  where  this  slope  would  take  up  too 
much  of  the  ground  within  the  defences  it  is  replaced  by  a 
wall,  termed  the  parade  wall,  which  rises  from  the  level  of 
the  interior  ground,  termed  the  parade,  to  the  interior  line 
of  the  tcrrcplcin. 

49... Inclined  planes  of  earth,  termed  ramps,  lead  from 
the  parade  to  the  tcrrcplcin,  being  placed  against  the 
rampart-slope  or  the  parade  wall.  The  ramps  are,  in  some 
cases,  terminated,  inwardly,  with  the  same  slope  as  that  of 
the  rampart;  in  others,  this  slope  is  replaced  b}-  a  wall, 
which  rises  to  the  top  surface  of  the  ramp,  or  a  little  above 
it. 

50... The  parapet,  serving  the  same  purposes  in  perma- 
nent as  in  field  w^^,  receives  the  same  general  form  as  in 
the  latter.  lu  some  cases,  the  exterior  slope,  PI.  3,  Fig.  12, 
is  replaced  b}'  a  wall,  which,  resting  on  the  to])  of  the 
8car[i  wall,  rises  to  the  level  of  the  sujierior  slope.  The 
exterior  slope  of  the  parapet  usually  rises  from  the  top  of 
the  scarp  wall,  leaving  a  narrow  berm  between  it  and  the 
scarp  or  f«e  of  the  wall.  In  some  cases,  it  is  thrown  so 
far  to  thcMenr  of  the  scarp,  PI.  3,  Figs.  9,  10,  as  to  leave 
suflic^|^^B£)m  for  a  communication,  C,  in  front  of  the 
par!^^^E^HBic-h  the  troops  can  circulate  under  cover  from 
fire,   ucTng^Bfekcd  cither  by  an  earthen  parajict,  or  by  a 


38  COMPONENT   ELEMENTS    OF    PERMANENT   WORKS. 

wall,  D.  This  covered  communication,  C,  is  termed  an 
exterior  corridor,  or  chcmin-dc-rondcs. 

51...T]ie  scarp  wall,  C,  PI.  3,  Figs.  4,  G,  retains  the  earth 
of  the  rampart  and  parapet,  and  forms,  by  its  height  and 
steepness,  the  chief  obstacle  to  an  open  assault.  The  top 
stone  of  the  wall,  A",  termed  the  cordon,  or  cojying,  projects 
be^'ond  its  face,  and,  serving  as  a  larmier,  or  drip,  protects 
it  from  the  effects  of  the  rain-water  which  runs  from  the 
parapet  upon  the  coping. 

52... The  line  in  which  the  face  of  the  scarp  wall,  pro- 
longed, would  intersect  the  coping,  is  termed  the  magistral. 
This  is  a  very  important  line  in  drawing  the  plans  of  per- 
manent works,  serving  as  the  directing  line  to  fix  (both 
upon  the  drawing  and  upon  the  ground  in  setting  out  the 
work)  the  dimensions  and  relative  positions  of  all  the 
bounding  lines  of  the  parapet  and  other  parts. 

53... The  counterscarp  wall,  G,  renders  the  ditch  of  more 
diiBeult  access  from  without  than  an  earthen  slope  would ; 
and,  when  of  sufficient  height  and  steepness,  it  forms  a 
very  serious  obstacle  to  an  open  assault.  It  receives  the 
same  general  forms  as  the  scarp  wall. 

54... The  glacis,  F,  is  of  the  same  form,  and  serves  the 
same  purposes  as  in  field  works;  but,  besides  these,  it  is 
indispensable  as  a  mask  for  the  scarp  wall,  covering  it  from 
distant  batteries,  in  cases  where  it  rises  above  the  level  of 
the  counterscarp,  and  thus  forcing  the  assailant  to  construct 
his  batteries  along  the  crest  of  the  glacis,  to  obtain  a  posi- 
tion from  which  the  scarp  wall  can  iTb*  lu'cachcd.  When 
the  glacis  serves  only  as  a  mask,  and  to  bring  the  assailant, 
as  he  rushes  forward  in  an  open  assault,  better  under  fire, 
it  is  In-ought  in  so  as  to  rest  on  top  of  the  counterscarp 
wall.  J  Jut  in  cases  where  a  covered  communication  is 
needed  beyond  the  ditch,  the  glacis  is  thrown  outward  for 
enough  to  leave  the  requisite  space  between  •t  and  the 
counterscarp.  This  sheltered  position  is  termedwe  covered- 
mag.  It  serves  both  for  the  circulation  of  the  tr(^)s,  from 
point  to  })oint,  and  as  a  defensive  position  ;  tjlije^jpOTt' ot' the 


COMPONENT   ELEMENTS    OF    PERMANENT   WORKS.  39 

glacis  facing  the  covered-way  being  arranged,  for  this  latter 
purpose,  like  an  ordinary  earthen  parapet. 

55. ..Mounds  of  earth  which  are  formed  solely  with  a 
view  to  mask  a  scarp  wall  from  fire  are  termed  face  covers. 
They  may  be  either  in  the  form  of  a  glacis,  or  receive,  on 
each  side,  the  slope  which  the  earth  would  naturally  take, 
sufficient  height  and  thickness  being  given  to  them  to 
subserve  the  object  to  be  attained. 

56... Among  the  modifications  of  the  usual  profile  is  the 
one  represented  in  PI.  3,  Fig.  11,  where  the  scarp  wall, 
rising  only  to  the  level  of  the  site,  is  surmounted  by  a 
parapet  wall,  D.  which  covers  a  chemin-de-rondes,  C.  This 
part  of  the  work  is  termed  a  fausse-braie.  By  dividing  the 
entire  height  of  scarp  wall  into  two  parts,  thus  rendering 
each  more  accessible  to  an  open  assault,  and  by  exposing 
the  troops  in  it  to  injury  from  the  splinters  from  the  scarp 
wall  behind  them,  caused  by  the  fire  of  the  assailant,  the 
fausse-braie  has  fallen  into  disuse. 

57. ..The  introduction,  within  the  last  thirty  years,  of  the 
bai-bette  gun-carriage,  now  in  general  use  for  permanent 
works,  has  led  to  a  modification  in  the  form  of  the  profile, 
with  a  view  of  better  adapting  it  to  the  new  carriage. 
This  change  is  shown  in  PI.  3,  Fig.  4,  and  consists,  mainly, 
in  raising  the  level,  de,  of  the  terreplein  fifteen  inches, 
placing  it  thus  at  six  feet  nine  inches  below  the  interior 
crest,  for  a  distance  of  twenty  feet  back  from  this  crest, 
and  connecting  it  by  a  slope,  cd,  of  45°  with  the  level 
below;  the  parapet  receives  an  interior  slope,  A^,  of  45°, 
which  fiills  upon  a  banquette,  fg,  for  infiintry,  the  tread  of 
which  is  two  feet,  and  is  placed  at  four  feet  six  inches 
below.  A,  the  interior  crest.  The  banquette-slope,  r/,  is  two 
base  to  one  peq:>endicular,  and  falls  upon  the  raised  portion, 
de,  of  the  terreplein.  When  it  is  necessary  to  place  guns 
in  battery  along  any  portion  of  a  parapet  having  this  form 
of  profile,  the  interior  slope  is  cut  down,  nearly  pei-pen- 
dicularly,  to  the  level  of  the  raised  portion  of  the  terre- 
plein, and  faced  with  fascines;  the  earth  between  this 
raised  portion  and  the  new  interior  slope  being  removed,  a 


40  COMPONENT    ELEMENTS    OF    TEKMANEXT    WORKS. 

level  and  solid  bed  is  ready  to  receive  the  carriages.  The 
surplus  earth  that  has  to  be  removed  by  this  operation 
can  be  used  for  ordinary  traverses,  and  for  increasing  the 
height  of  the  merlons  when  the  parapet  is  pierced  for 
embrasures, 

58... The  dimensions  and  forms  of  the  different  parts  of 
the  profile  are  so  established  as  to  afford  security  against 
an  open  assault ;  sufficient  command  of  the  parapet  over 
the  exterior  ground  to  sweep  it  efi'ectually  by  its  fire ;  cover 
from  the  fire  of  the  assailant ;  and  ample  room  with  suit- 
able arrangements  for  the  delivery  of  the  fire  of  the  assailed. 

59... Scarp.  A  scarp  wall,  30  feet  high,  is  usually  admit- 
ted as  a  sufficient  protection  in  dry  ditches  against  an 
escalade. 

This  rule,  drawn  from  the  experience  of  sieges,  and  the 
opinions  of  the  most  eminent  engineers,  seems  a  safe  one  ; 
since  to  scale  a  wall  of  this  height  would  require  ladders  of 
sufficient  length  to  enable  the  men  who  ascend  to  step  from 
the  ladder,  when  planted  securely  against  the  wall,  on  the 
coping,  and  of  sufficient  strength  to  bear  the  weight  of  six 
or  eight  men  mounting  together. 

To  carry  forward  ladders  of  the  dimensions  requisite  for 
this  purpose  and  place  them  in  position,  with  that  prompti- 
tude upon  wliicli  the  success  of  an  open  assault  must 
mainly  depend,  would,  of  itself,  be  an  operation  of  no  slight 
difficulty ;  but,  when  it  is  considered  that  the  assailants  are 
exposed  to  the  fire  of  the  defences  before  reaching  the  ditch, 
which  from  its  width  and  depth  alone  renders  it  a  serious 
obstacle,  and  that  after  they  have  entered  the  ditch  they  are 
still  under  the  fire  by  whicli  it  is  flanked,  it  is  difficult  to 
imagine  how  the  attempt  could  succeed  if  the  assailed  oftcr 
even  an  ordinary  degree  of  resistance. 

60... For  wet  ditches  filled  to  the  depth  of  six  feet,  and 
thus  secured  from  being  passed  by  fording,  a  height  of 
scarp  of  24  feet  is  considered  sufficient  security  from  an 
open  assault. 

61... Solid  scarp  walls,  with  ordinary  counterforts,  D,  re- 
ceive the  thickness  requisite  to  sustain  the  pressure  of  the 


COMPONENT   ELEMENTS    OF    PERMANENT   WORKS.  41 

earth  resting  against  their  hack.  The  hatter  given  them  on 
their  face  varies  in  different  services.  In  Vauban's  profiles 
the  hatter  is  |,  or  fiv^e  perpendicular  to  one  base.  In  Cor- 
montaingne's  it  is  f.  But  from  the  effects  of  time,  as 
observed  in  the  works  built  bj  these  engineers,  the  slopes 
of  their  walls  are  too  great.  In  tlie  French  service,  a  slope 
of  ^j^  is  now  usually  given.  In  the  Austrian, ',2  •  r^^^d  j,^  q^j. 
own,  from  ^j"*  to  '*^^.  In  this  diversity  of  practice  it  is  only 
necessary  to  remark,  that  the  stee[)er  walls  are  better  pro- 
tected from  the  effects  of  the  weather,  and  this  is  a  very 
important  consideration  in  structures  demanding  great 
durability. 

62... Parapet.  The  essential  properties  of  the  parapet  are 
to  afford  cover,  and  facilities  for  sweeping  the  ground  exte- 
rior to  it  by  the  artillery  and  musketry.  Its  form  and 
dimensions  are,  therefore,  so  adjusted  as  to  fulfil  these 
requirements. 

03... For  the  service  of  the  artillery,  barbettes  are  con- 
structed behind  the  parapet,  and  suitably  arranged  either 
for  guns  mounted  on  the  ordinary  travelling  carriages,  or 
upon  the  traversing  carriages,  which,  within  some  years 
back,  have  been  introduced  for  the  armament  of  land  and 
sea-coast  fronts ;  and  embrasures  are  pierced  in  the  parapet 
for  like  purposes. 

64... As  the  sole  of  the  embrasure  is  usually  not  more  than 
three  feet  below  the  superior  slope,  and  generally  parallel 
to  it,  care  must  be  taken  so  to  adjust  its  position  Avith 
respect  to  the  coping  of  the  scarp  wall  thjit,  when  the  guns 
are  fired  under  the  same  depression  as  the  superior  slope, 
the  balls  shall  clear  the  edge  of  the  coping  sufficiently  to 
prevent  its  being  injured  by  negligent  firing.  This  require- 
ment will  serve  to  determine  the  least  height  of  the  parapet 
above  the  coping,  and  which  may  be  done  by  cither  of  the 
following  methods. 

6o... Supposing  the  parapet  to  be  formed  of  earth  of  the 
ordinary  character,  IM.  4,  Fig.  14,  in  which  the  natural 
slope  is  45°,  or  { ;  the  superior  slope,  which  is  the  same  as 
that  of  the  embrasure  sole,  is  I,  the  one  usually  adopted  as 


42  COMPONENT    ELEMENTS    OF    PERMANENT    WORKS. 

the  greatest  for  the  parapets  of  permanent  works  ;  the 
thickness  of  the  parapet  18  feet,  tlie  least  given  to  it  to 
resist  the  heaviest  calibre  thus  far  employed  ;  and  that  a 
berm  of  two  feet  is  allowed  on  the  top  of  the  scarp  wall, 
between  the  edge  of  the  coping  and  the  foot  of  the  exterior 
slope  :  let  a  horizontal  line,  a  b,  be  first  drawn  at  the  level  of 
the  coping,  and,  from  its  exterior  edge,  a,  a  second  line,  a  c, 
making  an  angle  of  ^  with  ab;  this  last  line  will  be  the 
direction  of  a  shot  fired  under  the  depression  of  ^,  Avliich 
would  just  graze  the  edge  of  the  coping,  and  may  ])e  as- 
sumed as  the  lowest  position  that  the  sole  of  an  embrasure 
can  receive  ;  a  line,  therefore,  drawn  parallel  to  ac  and  3 
feet  above  it,  will  be  the  lowest  position  also  of  the  superior 
slope.  If  a  line  is  now  drawn  through  e,  the  interior  edge 
of  the  berm  and  the  foot  of  the  exterior  slope,  making  an 
angle  of  |  with  a  b,  it  will  be  the  direction  of  the  exterior 
slope  ;  and  the  point  m,  where  it  cuts  the  direction  of  the 
superior  slope,  wall  be  the  exterior  crest  of  the  parapet. 
Setting  ott"  along  the  horizontal  line  through  ni  tlie  thick- 
ness of  the  parapet,  or  18  feet,  and  erecting  a  vertical  at  the 
point  thus  determined,  the  point  7i,  where  this  vertical  cuts 
the  superior  slope,  will  give  the  position  of  the  interior 
crest,  w,  and,  consequently,  will  determine  its  vertical  height 
above  the  coping. 

66... The  following  simple  calculation  will,  in  like  man- 
ner, give  the  same  result.  Denote  by  x  the  base  ed=dm  of 
the  exterior  slope.  As  the  berm  a  c=2  feet,  the  thickness 
of  the  parapet  db='l8  feet;  the  distance  a  b^^a e-\-e d-\-d b^= 
2'+a:+18'=x+20';  but  since  the  line  ac  makes  an  angle  of 
^  with  a  b,  the  point  c,  where  it  cuts  the  vertical  through  d, 
will  make  6c=i  ab,  and,  as  from  the  position  of  the  supe- 
rior slope  and  the  thickness,  18  feet,  given  to  the  parapet, 
the  point  n  is  three  feet  above  the  points  in  and  e,  it  follows 
that  bc^^dm=^x.  Therefore,  from  the  two  preceding  equa- 
tions there  obtains  x=i  (a:+20');  hence  x=4  feet.  From 
this  value  of  x,  the  height  6  c  of  ??,  above  the  point  a,  is  7 
feet;  which,  under  the  assumed  conditions,  is  the  least 
height  of  tlie  interior  crest  above  the  coping  in  which  a 


COMPONENT    ELEMENTS    OF    PERMANENT    WORKS.  43 

ball,  passing  in  tlie  same  line  as  the  sole  of  the  embrasure, 
would  just  touch  the  exterior  edge  of  the  coping.  In 
order  to  secure  the  coping  from  damage,  the  interior  crest 
is  placed  8  feet  above  it. 

It  should  l)e  observed  that  the  result  here  arrived  at, 
being  dependent  on  the  assumed  data,  will  vary  by  chang- 
ing the  elements  of  the  problem. 

67... The  height  of  8  feet  thus  determined,  as  the  least 
which  the  parapet  should  receive  above  the  magistral,  is 
advantageous  both  as  to  economy  and  for  the  defence,  and, 
therefore,  should  not  be  exceeded  except  for  good  reasons. 
This  will  be  apparent,  when  it  is  considered  that  the  pres- 
sure on  the  scarp  wall,  from  the  weight  of  the  parapet, 
increases  with  the  height  of  the  latter,  and  that  the  wall 
must  be  made  stronger  in  proportion ;  and,  although  an 
increased  height  of  parapet,  by  increasing  the  obstacle  to 
an  escalade,  is  in  favor  of  the  defence,  still,  when  it  much 
exceeds  8  feet,  the  assailant,  on  reaching  the  top  of  the 
wall,  will  find  shelter  from  the  tire  of  the  parapet,  which 
will  pass  above  his  head,  and  he  will  be  better  enabled  to 
reach  the  top  of  the  parapet  than  when  partly  exposed  to 
this  fire,  as  he  will  be  in  low  parapets. 

68. ..The  inclination  of  ^  has  been  generally  adopted  as 
the  greatest  inclination  of  the  superior  slope,  both  on  ac- 
count of  the  greatest  depression  that  guns  can  be  fired 
under  without  straining  too  much  the  carriages,  and  to 
avoid  making  the  iiortion  of  the  parapet  near  the  interior 
crest  so  weak  that  it  could  be  readily  destroyed,  and 
the  troops  and  materiel  exposed  to  view.  "Whenever  the 
field  of  fire  will  admit  of  it,  it  will  prove  advantageous, 
under  these  two  points  of  view,  to  give  a  smaller  inclina- 
tion to  the  superior  slope.  In  cases  where  it  is  desirable 
to  reach  some  point,  by  the  fire  requiring  a  greater  slope 
than  ^,  it  may  be  done  without  inconvenience  if  the  para- 
pet is  not  likely  to  be  exposed  to  a  heavy  fire,  a  suital)le 
inclination  being  also  given  to  the  gun-platform. 

69... The  exterior  slo})e,  for  the  reasons  given  in  discuss- 
ing the  parapets  of  field  works,   should    not  be   less,  on 


44  COMPONENT   ELEMENTS    OF    PERMANENT   WORKS. 

land  fronts,  than  the  natural  slope  of  the  earth  of  which 
the  parapet  is  formed.  In  sea-coast  works,  where  the  para- 
jtet  18  high,  and  can  he  reached,  within  cannon  range,  only 
l»y  elevating  the  guns  of  the  ships,  the  exterior  slope  may- 
be replaced  by  a  vortical  revetenient  of  stone,  or  one  of  sods 
with  but  a  slight  inclination,  as,  from  the  direction  of  the 
fire,  this  facing,  even  if  partiallj-  destro^-ed,  will  not  cause 
such  weakness  in  the  parapet  as  to  expose  the  troops.  By 
using  a  facing  of  this  kind,  the  parapet  will  occupy  less 
room  and  leave  more  interior  space,  which,  in  small  works, 
is  often  desirable. 

70... As  a  berm  of  two  feet  aflbrds  a  tolerable  landing  to 
the  assailant  in  an  escalade,  it  w^ould  be  better  to  make  it 
less,  particularly  on  fronts  open  to  such  an  assault.  The 
usual  berm  may  be  given  when  the  work  is  constructed, 
and  be  afterward  lessened  by  increasing  the  thickness  of 
the  parapet  when  the  w^ork  is  to  be  placed  in  a  defensive 
attitude. 

71... The  thickness  of  the  parapets  of  ordinary  earth  sel- 
dom exceed  20  feet.  This  is  the  dimension  usually  given 
in  European  constructions  of  important  works  liable  to  a 
long  exposure  to  fire,  and  has  been  found,  by  experience, 
to  aftbrd  good  cover  against  a  well-nourished  and  pro- 
tracted fire  of  the  heaviest  calibre  thus  far  used.  In  our 
service,  a  thickness  of  18  feet  has  been  more  usuall}'  given. 
For  less  important  works,  and  particularlj'  where  parapets 
are  not  likely  to  be  systematically  battered,  the  thickness 
may  be  safely  reduced  to  12  or  15  feet. 

72... In  the  form  of  profile  given  in  PI.  3,  Fig.  4,  the  por- 
tion of  the  terreplein  on  which  the  guns  rest  in  battery  is 
placed  at  a  level  below  the  interior  crest,  to  admit  the  guns 
being  fired  over  the  parapet;  and  this  difterence  of  level  is 
sufficient  to  give  good  cover  along  the  parapet  to  the  men 
serving  the  guns.  The  portion,  b  c,  of  the  terreplein  to  the 
rear  of  this  serves  as  a  communication  along  the  line  of 
fortification,  and,  being  further  back,  should  be  somewhat 
lower,  to  attbrd  good  cover  from  shot  just  passing  over  the 
interior  crest.     It  is  usually  placed  at  a  level  of  8  feet 


COMPONENT    ELEMENTS    OF    PERMANENT    WORKS.  45 

below  the  interior  crest;  a  slope  of  one  foot  inward  being 
givcii  to  it,  estimating  it  from  the  line  of  the  interior  crest 
to  the  exterior  edge  of  the  terreplein,  to  free  it  rapidly 
from  the  rain-water.  This  level,  however,  may  be  lowered 
if  the  irreguharity  of  the  site  requires  it,  from  the  com- 
mand the  exterior  ground  may  have  over  the  work.  In  all 
cases  it  will  be  rather  a  question  of  economy,  to  be  decided 
by  the  amount  of  excavation  and  embankment.  As  the 
space  in  question  serves  chiefly  the  purposes  of  a  commu- 
nication, it  may  be  reduced,  through  motives  of  economy, 
to  a  width  which  will  be  sufficient  for  the  o-un-carriatres 
and  other  vehicles  employed  in  the  defence  to  pass  each 
other.  For  this  pnrpose  the  entire  width  of  the  terreplein, 
estimating-  it  between  the  verticals  throuo;h  the  interior 
crest  of  the  parapet  and  the  crest  of  the  rampart-slope,  has 
usually  received  42  feet  in  enceintes  of  importance  where  a 
circulation  of  the  kind  just  mentioned  is  to  be  provided 
for.  In  other  cases  it  may  be  reduced  to  24,  or  even  20 
feet.  It  should  be  remarked,  however,  that  as  a  wide  terre- 
plein facilitates  the  disposition  of  troops  for  an  active 
defence  of  the  breach,  it  should  not  be  too  much  reduced 
along  those  portions  of  the  enceinte  exposed  to  be  opened. 

73... The  rampart  toward  the  parade  usually  receives  a 
slope  greater  than  that  which  the  earth  would  naturally 
assume  where  the  interior  space  admits  of  it.  This  will 
offer  the  means  of  forming  narrow  foot-paths  along  this 
slope  leading  from  the  parade  to  the  terreplein  at  con- 
venient points,  and  prevent  the  slope  from  being  injured, 
which  it  is  apt  to  be  by  the  men  wearing  such  short  cuts  for 
themselves.  Where  the  interior  space  would  be  too  much 
circumscribed,  this  slope  may  be  replaced  by  a  parade 
wall. 

74. ..The  banquette-tread  and  the  interior  slope,  as  shown 
in  PI.  3,  Fig.  4,  will  answer  sufficiently  well  for  ordinary 
purposes;  but  where  a  warm  fire  in  two  ranks  is  to  be 
sustained,  the  interior  slope  should  be  trimmed  down  to  the 
same  given  to  it  in  field  works,  which  will,  at  the  same 
time,   enlarge   the   banquette-tread   so   as  to   receive   two 


46  COMPONENT    ELEMENTS    OF    PERMANENT    WORKS. 

ranks.  It  would  be  well,  also,  in  making  these  changes  for 
an  active  defence,  to  raise  the  banqnette-tread  to  within  a 
level  of  4^  feet  of  the  interior  crest,  for  the  greater  conve- 
nience of  short  men  in  delivering  their  fire. 

75... The  command  of  the  parapet  over  the  site  has  a  very 
important  bearing  in  the  defence  of  permanent  works,  as 
the  assaihmt  meets  wuth  the  more  difficulty,  in  running 
forward  his  trenches,  as  the  fire  of  the  defences  becomes 
more  plunging.  Motives  of  economy,  however,  require 
the  command  to  be  restricted  within  quite  narrow  limits. 
When  the  work  consists  of  a  simple  enceinte,  enveloped 
by  a  covered-way,  the  command  may  be  reduced  to  16  feet, 
allowing  a  command  of  8  feet  to  the  interior  crest  of  the 
glacis  over  the  site,  and  a  height  of  8  feet  to  the  interior 
crest  above  the  coping,  which,  with  the  rest  of  the  scarp 
wall,  to  be  masked  by  the  glacis,  must  not  rise  above 
the  level  of  its  interior  crest.  Where  there  are  other 
outworks  besides  the  covered-way  in  defensive  relations 
with  the  enceinte,  the  latter  cannot  receive  a  command 
over  the  site  of  less  than  about  20  feet,  in  order  to  give 
it  a  suitable  command  over  the  whole  of  the  outworks. 

76... Counterscarp  Wall.  A  revetted  counterscarp  is 
regarded  as  adding  to  the  difficulty  of  descending  into  the 
ditch,  and  as  oti:ering  greater  security  against  an  open 
assault.  For  this  purpose  the  wall  should  not  be  less 
than  12  or  15  feet  in  height,  to  offer  a  serious  impediment; 
in  any  case  where  motives  of  economy  do  not  imperiously 
demand  it,  the  counterscarp  wall  of  the  enceinte  should 
be  from  18  to  24  feet  in  height.  This  height  will  not  only 
give  e:reat  security  to  the  ditch,  but,  as  will  be  seen  in 
the  description  of  the  siege  works  of  the  assailant,  it  will 
delay,  considerably,  his  progress,  as  the  gallery  by  which 
he  must  generally  reach  the  bottom  of  the  ditch  from  the 
level  of  the  covered-way  terreplein,  is  one  of  the  slowest 
and  most  laborious  of  his  operations. 

77... Ditch.  The  width  and  depth  of  the  enceinte  ditch 
depends  mainly  upon  the  amount  of  embankment  required 
for  the  enceinte  and  the  glacis,  and,  therefore,  \\\\\  result 


COMPONENT    ELEMENTS    OF    PERMANENT    WORKS.  47 

from  the  calculation  for  equalizing  the  excavation  and  em- 
bankment which  these  demand.  A  deep  and  narrow  ditch 
offers  the  advantage  of  presenting  more  difficulty  to  the 
assailant  in  reaching  the  bottom  of  it;  and,  from  the  position 
he  is  obliged  to  take  up  for  his  breach  batteries  to  open  the 
scarp  wall,  his  fire  cannot  see  the  wall  so  near  its  foot  as  in 
a  wide  ditch,  and  the  breach,  therefore,  may,  from  this 
cause,  be  less  practicable.  A  wide  ditch,  on  the  other 
hand,  requires  more  labor  to  construct  the  trench  across  it, 
by  which  the  assailant  can  reach  the  foot  of  the  breach 
under  cover.  This  is  a  consideration  of  some  importance 
in  w^et  ditches,  where  the  assailant  is  obliged  to  construct  a 
dike,  upon  which  the  parapet  of  his  cover  is  placed.  In 
the  practice  of  engineers  the  enceinte  ditch  has  received  a 
width  of  from  20  to  30  yards  when  dry,  and  from  30  to  45 
yards  when  wet.  These  dimensions  may  bo  reduced  to 
within  10  or  12  yards,  where  the  embankments  are  not 
great  and  circumstances  are  unfavorable  to  an  attempt 
at  escalade. 

78. ..The  bottom  of  the  ditch  usually  receives  a  slight 
slope  from  the  foot  of  the  scarp  and  counterscarp  to  its 
centre,  where  a  small  drain,  termed  a  cunette,  is  dug  to 
receive  the  surface  water  and  keep  the  ditch  dry.  In  some 
cases,  from  motives  of  economy,  the  difference  of  level 
between  the  cunette  and  the  foot  of  the  counterscarp  walls 
is  increased,  thus  giving  a  less  height  of  wall.  This  prac- 
tice, however,  can  only  be  followed  where  the  Inundations 
of  the  wall  will  be  secure  from  the  soil  of  the  bottom  of  the 
ditch  being  of  such  a  nature  as  not  to  yield  from  the  effects 
of  the  weather  upon  it. 

79... General  Remarks.  The  rules  here  given  with  re- 
spect to  the  form  and  dimensions  of  the  general  profile  of 
the  enceinte  are  founded  upon  reasons  growing  out  of  the 
nature  of  the  question,  and  as  such  have  served  as  guides  to 
engineers  in  the  practice  of  their  profession.  As  they  have 
stood,  besides,  the  test  of  long  experience,  it  is  safe  to  follow 
them,  whilst  at  the  same  time  the  engineer  should  not  hesi- 
tate to  vary  from  them  when  satisfied,  after  careful  exami- 


48  COMPONENT    ELEMENTS    OF    PERMANENT    WOPJvS. 

nation,  that  tlie  case  before  him  requires  it.  Fortification, 
it  must  be  remembered,  is  like  all  other  arts.  It  has  its 
canons  which  are  founded  upon  the  nature  of  the  question, 
and  its  rules  of  practice  based  upon  these  and  upon  expe- 
rience. As  the  latter  presents  to  the  engineer  new  facts,  his 
practice  must  be  made  to  conform  to  them,  but  the  general 
principles  of  his  art  must  ever  remain  the  same  aiid  be  his 
invariable  guide. 

OPEN  DEFENCES. 

80... By  this  term  is  understood  the  dispositions  made  for 
the  action  of  the  troops  and  armament  which  are  covered 
from  the  missiles  of  the  assailed  by  the  parapet  alone. 

81... To  this  class  belongs  the  arrangement  of  the  parapet 
Avhich  has  already  been  described;  simple  loop-holed  ■walls  for 
musketry,  used  as  enclosures  of  gorges,  etc. ;  exterior  corridors 
which  are  covered  either  by  a  wall  or  an  earthen  parapet ; 
and  barbettes  and  embrasures  for  artillery. 

82... Loop-holed  Walls.  Walls  of  this  class  when  used  as 
the  enclosures  of  the  gorges  of  lunettes  or  other  isolated 
works,  placed  in  advance  of  the  enceinte,  but  within  the 
reach  of  its  artillery  fire,  should  be  high  enough  to  secure 
the  work  from  an  open  assault,  and  sufficiently  thick  to 
resist  the  occasional  shot  which  may  reach  them  over  the 
parapet  by  which  they  are  covered.  For  these  purposes  the 
height,  PL  4,  Fig.  24,  should  be  from  12  to  15  feet,  and  the 
thickness  from  4  to  5  feet.  The  loop-holes  are  not  placed 
nearer  to  each  other  than  from  3  to  4  feet,  estimated  between 
their  axes.  They  should  be  at  least  6  feet  above  the  exterior 
foot  of  the  wall,  and  4^  feet  above  the  ground  or  banquette 
within.  The  loop-holes  are  usually  placed  at  regular  inter- 
vals along  the  line  of  the  wall ;  or  only  opposite  that  portion 
of  the  exterior  ground  upon  which  a  fire  is  to  be  brought  to 
bear. 

83... The  form  and  dimensions  of  the  loop-hole  will  de- 
pend upon  the  thickness  of  the  wall  and  the  field  of  view, 
both  vertically  and  horizontally,  which  is  to  be  covered  by 
its  fire.     The  plan  is  either  trapezoidal,  PI.  4,  Figs.  17,  20, 


COMPONENT    ELEMENTS    OF    PERMANENT    AVORKS. 


49 


widening  from  the  front  of  the  wall  inward,  or  else  it 
widens  from  the  centre  each  way  to  the  front  and  back;  or, 
as  is  the  more  usual  form  in  our  works,  the  interior  portion 
from  the  centre  widens  inward,  whilst  the  exterior  ]>art  is 
rectangular  in  plan.  The  first  form  is  l)est  adapted  to  walls 
not  more  than  2 J  feet  thick  ;  the  others  to  lieavier  walls  ;  the 
object  being  to  lessen,  as  far  as  practi('al)lo,  the  weakness 
which  loop-holes  necessarily  cause  to  the  wall ;  this  defect 
increasing  as  the  exterior  or  interior  opening  is  greater. 

84... For  thin  walls,  where  the  plan  of  the  loop-hole  is 
trapezoidal,  the  width  of  the  exterior  opening  may  be  from 
2  to  4  inches,  and  that  of  the  interior  from  15  to  18  inches. 
These  dimensions,  however,  may  vary  according  to  the  field 
of  fire  to  be  brought  within  the  range  of  the  loop-hole,  the 
more  or  less  cover  to  be  given  to  the  troops,  and  the  strength 
of  the  masonr}'  of  which  the  wall  is  formed.  The  vertical 
dimensions  of  the  loop-hole,  both  on  the  interior  and  the 
exterior,  will  depend  upon  the  field  of  fire  to  be  embraced  in 
this  last  direction,  and  they  will  be  regulated  accordingly; 
the  slope  of  the  top  and  sole  of  the  loop-hole  receiving  a 
suitable  slope  or  direction  for  this  purpose. 

The  foregoing  details  can  only  be  well  determined  upon 
from  the  special  object  to  which  the  loop-holed  defences  are 
to  be  applied.  Care  only  is  to  be  taken  that,  in  attempting 
to  give  cover  to  the  troops,  their  field  of  view  be  not  too 
restricted,  by  too  narrow  an  opening  for  tlie  use  of  the  fire- 
arms. 

85...  Where  the  throat  or  narrowest  part  of  the  loop-hole 
is  within  the  wall,  the  exterior  opening 
leaves  a  Avider  mark  for  the  missiles  of 
the  assailed  ;  and  when  the  sides  of  the 
loop-hole  gradually  widen  outward  a  shot 
striking  one  of  them  may  glance  inward 
and  do  injury.  To  prevent  this  accident 
the  sides  and  sometimes  the  sole  are  made 
in  offsets.  This,  however,  is  not  so  con- 
venient a  mode  of  constructing  the  loop-hole,  nor  one  so 
efficient  in  arresting  the  shot  which  do  not  directly  attain 


50  COMPONENT   ELEMENTS   OF    PERMANENT   WORKS. 

tlie  throat,  as  tlie  one  in  tlio  annexed  Figure,  wliicli  is  tlie 
plan  of  one,  taken  from  our  works,  pierced  in  a  wall  6  feet 
thick.  The  plan  of  the  exterior  portion,  a,  is  rectangular, 
the  exterior  widtli  2  feet ;  the  throat  is  at  the  centre  of  the 
wall,  and  6"  wide;  the  interior  portion,  b,  is  trapezoidal, 
and  2  feet  wide  on  the  interior, 

86... In  open  exterior  corridors  the  loops  are  covered  in 
front,  either  by  an  earthen  parapet,  which  is  usually  only 
musket-proof,  the  scarp  wall  being  run  up  to  the  superior 
slope,  or  else  the  scarp  wall  serves  as  the  cover,  in  which 
case  it  is  pierced  either  throughout  its  length  or  at  suitable 
points  with  loop-holes.  The  floor  of  the  corridor,  C,  PI.  4, 
Fig.  27,  serves  as  a  banquette-tread  for  the  loop-holes,  and 
is,  therefore,  placed  with  reference  to  the  direction  of  the 
fire  from  the  loop-holes.  The  height  at  which  the  scarp  wall 
rises  above  the  floor  of  the  corridor  will  depend  upon  the 
level  of  the  floor  and  that  of  the  bottom  of  the  ditch  ;  this 
height,  however,  should  not  be  less  than  6|  feet,  to  aflbrd 
sufficient  cover  to  the  troops. 

87... Scarp  walls  of  this  arrangement  are  termed  semi- 
detached, to  distinguish  them  from  the  ordinary  retaining 
scarp  walls  and  those  in  which  the  wall  is  entirely  separated 
from  the  rampart,  serving  as  a  simple  enclosure  to  it  to 
prevent  an  escalade. 

88... The  preceding  Figure  is  given  as  an  example  of  a 
semi-detached  scarp.  A,  an  earthen  counterscarp,  and  cov- 
ered-way, D ;  being  a  section  of  an  outwork  of  one  of  our 
sea-coast  forts. 

89... Barbette  Batteries.  For  guns  mounted  on  the 
ordinary  field  and  siege  carriages,  the  barbettes  are  con- 
structed in  the  same  manner  and  with  the  same  dimensions 
as  in  field  works.  The  arrangement  of  the  ramps  and 
slopes  being  determined  by  the  position  in  which  the  bar- 
bette is  placed,  and  its  relative  position  with  respect  to  the 
terreplein  and  parapet. 

90... For  the  heavy  guns  used  in  forts,  both  for  sea  and 
land  fronts,  a  solid  foundation  of  stone  is  laid  to  receive 
the  pintle  and  rail,  upon  which  the  chassis  of  the  gun  is 
made  to  traverse.     This  foundation   consists    of  a   heavy 


COMPONENT   ELEMENTS    OF    PERMANENT   WORKS.  51 

block,  set  firmly  in  a  bed  of  beton,  to  which  the  pintle, 
phxced  at  the  centre  of  motion,  is  solidly  attached ;  and  of 
stone  blocks  set  in  like  manner,  to  which  are  firmly  attached 
the  iron  rails,  which  either  form  a  segment  of  a  circle,  as  in 
PL  7,  Figs.  54,  55,  or  a  complete  circle,  as  in  Figs.  50,  57, 
58,  npon  which  the  traverse-wheels  run. 

91... In  order  to  afford  the  gun  a  wide  traverse,  a  recess  is 
made  in  the  parapet  in  front  of  the  carriage,  of  sufficient 
dimensions  to  allow  the  mancpuvres  of  the  cliassis  and 
top  carriage  without  obstruction  ;  for  this  purpose  it  has 
received  a  depth  of  2  feet,  its  front  5  feet;  its  two  sides 
having  a  slant  of  30  inches  base  to  24:  inches  perpen- 
dicular. The  recess,  and  usually  the  entire  length  of  the 
battery  front,  is  faced  with  a  breast-height  wall  that  only 
rises  to  within  18  inches  of  the  top  of  the  parapet ;  its 
thickness  being  2  feet.  The  Figures  referred  to  give  the 
plan,  sections  and  elevation  of  the  barbette  arrangements  in 
question  adopted  in  our  service. 

92... Embrasure  Batteries.  The  embrasures  cut  in  the 
parapets  for  guns  on  field  and  siege  carriages,  difler  in  no 
essential  point  from  those  for  field  works.  It  is  Avell,  how- 
ever, to  observe,  as  the  parapet  is  weakened  by  receiving 
embrasures,  the  splay  given  to  them  should,  in  all  cases,  be 
carefully  regulated  ])y  the  field  of  fire  it  is  desirable  to 
command,  so  as  to  leave  as  large  a  mass  of  merlon  between 
each,  as  practicable,  to  resist  the  assailant's  fire. 

93. ..For  guns  mounted  on  sea-coast  carriages  the  embra- 
sures are  very  shallow,  merely  covering  the  gun  from  lateral 
view.  The  annexed  Figure  is  a  profile  of  the  enceinte 
through  the  axis  of  an  embrasure  of  recent  Frent-li  works, 
showing  the  manner  in  which  the  i)rofile  is  modified  and 
revetted  for  the  service  of  the  pieces. 


-\':—-/o Y-3-* -^^- '^- 


-^o-— 


62  COMPONENT    ELEMENTS    OF    PERMANENT    WORKS. 

94...ArACiiicouLTS.  For  the  purpose  of  attaining,  by  mus- 
ketry, tlie  foot  of  a  scarp  wall  without  iiank  defences,  resort 
must  ))e  had  to  a  machicouhxted  arrangevnent  at  the  top  of 
the  scarp. 

95. ..The  usual  mode  adopted  for  this  purpose,  PI.  8,  Figs. 
67,  68,  is  to  form  a  parapet  wall,  which  rests  upon  a  solid 
horizontal  band  of  stone,  near  the  top  of  the  scarp,  which 
is  supported  on  corbels,  or  projecting  blocks,  firmly  built 
into  the  wall.  The  back  of  the  parapet  wall  is  placed  a 
few  inches  in  advance  of  the  scarp,  leaving  room  for  the 
slanting  loop-holes  pierced  in  the  horizontal  band  through 
which  the  fire  is  to  be  delivered  on  the  foot  of  the  scarp. 
The  top  of  the  parapet  wall  is  also  arranged  to  admit  of 
firing  on  more  distant  points. 

96... In  the  example  given,  which  is  from  an  Austrian 
authority.  Fig.  67  is  a  front  elevation,  and  Fig.  68  a  section 
through  a  loop-hole. 

Figs.  65,  66,  are  a  front  elevation  and  section  through 
a  loop-hole,  from  the  same  authority.  This  is  a  semi-de- 
tached scarp  wall,  the  top  portion  of  which  is  arranged  on 
the  back  with  loop-holed  recesses ;  the  lower  portion  hav- 
ing very  inclined  arched  recesses  in  front,  with  slanting 
loop-holes  to  fire  on  the  foot  of  the  scarp  from  the  upper 
recesses. 

97... Where,  from  the  irregularity  of  the  site,  the  ordinary 
machicoulis  cannot  be  made  efficient,  resort  may  be  had  to 
small  polygonal  chambers  of  stone,  open  at  top,  and  hav- 
ing the  sides  and  bottom  pierced  with  loop-holes  and 
machicoulis.  These  constructions  may  be  made  just  of 
sufficient  size  to  hold  a  single  sentinel.  They  are  placed  at 
the  angles  of  the  works,  where  the}^  will  not  be  exposed  to 
artillery,  and  are  supported  on  a  corbel  work  projecting 
from  the  top  of  the  scarp  wall. 

COVERED  DEFENCES. 

98... Detached  Scarp  "Walls.  When  the  scarp  Avails  are 
entirely  detached,  leaving  an  open  corridor  between  them 


COMPONENT    ELEMENTS    OF    PERMANENT    AVOIIKS.  b6 

and  the  rampart,  they  arc  }»ierced  with  one  or  two  tiers  of 
loop-holes  from  which  a  lii-e  can  be  brought  from  the  ditch 
and  upon  the  terreplein  of  the  covered-wa}',  or  an}-  work 
in  front  of  the  enceinte. 

99. ..To  give  cover  to  the  men  at  the  loop-holes,  arched 
recesses,  PI.  4,  Figs.  25,  26,  are  made  in  the  thickness  of 
wall,  or  else  short  counterforts  are  built  back  from  the  wall 
which  serve  as  the  piers  of  covering  arches.  The  width  of 
the  recesses  should  admit  of  three  or  four  loop-holes  at  the 
usual  distance  apart;  their  height  and  depth  be  sufficient 
to  give  the  men  shelter  from  vertical  fire,  and  alh)\v  tliem 
to  handle  their  arms  with  convenience. 

100. ..The  two  Figures  above  are  sections  of  this  descrip- 
tion of  scarp  wall  taken  through  the  crowns  of  the  arches, 
as  shown  in  an  Austrian  work.  A,  is  a  section  of  the  wall; 
£  and  Z>,  elevations  of  the  sides  of  the  recess;  C,  an  eleva- 
tion and  section  of  the  recess  arch. 

101. ..Semi-detached  walls.  Fig.  28,  are  also,  in  some 
cases,  built  with  recesses.  Besides  these,  traverse  walls,  H, 
are  built  back  from  the  scarp  wall  into  the  parapet,  at  in- 
tervals, to  aftbrd  cover  to  the  troops,  circulating  in  the  cor- 
ridor, from  enfilading  fire,  and  to  admit  of  a  defence  of  the 
corridor  if  the  assailant  should  enter  it  between  anv  two  of 
these  traverses.  For  this  purpose  the}'  are  pierced  with 
loop-holes,  and  have  door-ways  for  circulation  tliroughout 
the  corridor. 

102... In  the  more  recent  fortifications  built  in  Germany 
and  the  north  of  Europe,  a  frequent  use  has  been  made  of 
detached  scarps.  They  present  a  double  obstacle  to  an  es- 
calade, as  the  assailant,  having  gained  the  top  of  the  wall, 
lias  still  to  descend  on  the  other  side.  They  would  proba- 
bly be  more  easily  breached  than  the  ordinary  scarp  rcvete- 
ments  with  counterforts;  and  from  some  experiments  made 
in  Fngland,  with  a  view  of  ascertaining  the  resistance  of 
these  walls  and  the  cover  given  them  by  earthen  mask.'^, 
arranged  in  a  manner  similar  to  some  of  the  German  forti- 
fications, it  is  questionable  whether,  with  the  heavier  cali- 
bre now  coming  into  use  in  sieges  and  tlie  improvement  of 


04  COMPONENT    ELEMENTS    OF   PERMANENT   WORKS. 

late  years  in  tlieir  range,  such  walls  niig-lit  not  be  readily 
breached  from  a  distance. 

103...  The  partly  detached  scarp  wall,  with  relieving 
arches,  would  seem  to  ofter  the  advantage  of  more  security 
from  escalade  than  the  old  scarp  wall,  as  the  assailed  are 
in  a  better  position  in  the  corridor  to  drive  the  assailant 
back  than  when  placed  behind  the  parapet.  It  offers  all 
the  difficulties  to  breaching  of  the  full  scarp  with  relieving 
arches,  and  presents,  when  the  breach  is  rendered  practica- 
ble, a  narrow  defile  through  which  the  assailant  must  force 
his  way  into  the  work;  whereas,  wdien  the  wholly  detached 
scarj)  is  overthrown,  the  assailant  may  enter  witli  any  front 
he  may  choose,  as  the  only  obstacle  then  in  his  way  will 
be  that  of  the  height  of  the  rampart  and  the  steepness  of 
its  exterior  slope. 

104... Scarp  Galleries.  In  the  permanent  works  ot 
more  recent  construction  in  our  own  country  and  in  Eu- 
rope, revetement  walls,  with  relieving  arches,  PI.  4,  Fig.  15, 
have,  in  most  cases,  been  introduced  instead  of  the  ordi- 
nary thick  walls,  with  counterforts,  which  had  been  hither- 
to the  usual  mode  of  retaining  the  earth  of  the  rampart 
and  parapet. 

105... The  piers  of  the  relieving  arches,  which  also  serve 
as  counterforts  to  the  revetement  wall,  are  rectangular  in 
plan,  and  usually  run  back  from  12  to  16  feet.  They  are 
from  4  to  6  feet  thick,  and  placed  from  12  to  18  feet  apart 
between  their  centre  lines.  The  arches  are  usually  full 
centre,  and  tw^o  feet  thick,  with  a  roof- shaped  capping, 
which  adds  an  additional  thickness  from  9  to  12  inches 
over  the  crown  of  the  arch. 

106. ..The  preceding  Figure  is  a  section  of  a  revetement 
wall  of  this  kind,  of  one  of  our  forts,  though  the  curtain 
in  front  of  which  is  a  mask,  of  which  D  is  the  section.  J5, 
is  an  elevation  of  the  face  of  the  pier;  C,  the  relieving 
ai'ch  ;  and  A,  the  scarp  wall. 

107... This  mode  of  construction  offers  the  advantages  of 
a  more  stal)le  structure,  and  rendering  it  more  difficult  for 
the    assailant   to    make    a  practicable   breach  in  the  wall, 


COMPONENT   ELEMENTS    OF    PERMANENT   WORKS.  55 

whilst,  by  a  suitable  arrangement  of  the  relieving  arches 
and  their  piers  with  the  earth  of  the  rampart,  a  sufficient 
space  can  be  secured  behind  the  scarp  wall  to  form  a  gal- 
lery for  defensive  purposes. 

108. ...The  arches  and  piers  form  the  top  and  sides  of  the 
gallery,  the  scarp  wall  forming  the  front,  and  the  back  or 
rear  being  either  partly  or  wholly  closed  ])y  a  wall  which 
retains  the  earth  behind  it.  The  gallery  is  thus  divided  up 
into  chambers,  the  communication  between  which  is  effect- 
ed b}'  door-ways  made  through  the  piers. 

109.... The  width  and  height  of  the  gallery  should  in  all 
cases  be  sufficient  to  allow  the  men  ample  room  for  hand- 
ling their  fire-arms,  and  to  admit  of  a  circulation  through 
the  gallery,  when  the  troops  for  the  defence  are  posted  in 
it. 

110.. ..From  three  to  four  loop-holes  are  made  in  the  por- 
tion of  the  scarp  wall  that  forms  the  front  of  each  chamber. 
The  dimensions  and  forms  of  the  loop-holes  are  the  same 
as  alreadj^  described,  and  they  are  otherwise  arranged  for 
defence  as  in  detached  scarp  walls. 

111... In  PI.  4,  Fig.  16,  a  section  of  a  scarp  gallery  con- 
structed in  one  of  our  forts  is  shown.  A,  is  the  scarp  wall ; 
J^,  the  pier  of  the  relieving  arch,  C;  D,  the  rear  wall  which 
closes  the  gallery  and  sustains  the  earth  behind  it.  The 
section  also  shows  the  parts  of  the  rampart  and  parapet, 
and  the  breast-height  wall,  E. 

112... In  Figs.  17,  18,  19,  the  plan,  section  and  rear  eleva- 
tion of  a  gallery  is  shown  as  given  in  French  authorities. 
The  peculiarity  of  this  example.  Fig.  19,  consisto  in  the 
arrangement  of  the  rear  of  the  gallery,  which  instead  of 
being  entirely  closed  by  a  wall  is  only  partly  so;  a  small 
wall,  a,  which  rests  upon  an  arch,  />,  built  between  the 
two  piers,  is  placed  parallel  to  the  back  of  the  scarj)  wall, 
and  at  a  distance  from  it  equal  to  the  width  of  the  gallery, 
the  top  of  the  wall  being  raised  to  the  level  of  the  surface 
of  the  earthen  slope,  which  falls  in  behind  from  the  top  of 
the  arch.  The  section.  Fig.  18,  through  r  s,  and  elevation, 
Fig.  19,  show  the  position  of  the  loop-holes,  and  the  vent 


56  CUMPOXEXT    ELEMEXTS    OF    I'ERMAXEXT    WORKS. 

for  the  escape  of  the  smoke,  whicli  is  pierced  in  the  scarp 
wall  just  below  the  crown  of  the  arch,  i?,  are  the  piers; 
A,  the  arches  with  tlieir  capping;  Z>,  the  door-ways  through 
the  piers. 

113... Figs.  20,  21,  represent  the  plan  and  section  of  a 
scarp  gallery  in  two  tiers,  as  given  in  an  Austrian  work. 
The  rear  of  the  gallery  is  closed  by  a  simple  wall.  Besides 
the  vent-holes  for  the  escape  of  smoke,  drains  are  made  in 
the  scarp  wall,  at  the  level  of  the  gallery  floor,  to  convey 
oft'  any  water  that  may  collect  in  it. 

114. ..Figs.  22,  23,  are  a  plan  and  section,  from  the  same 
authority,  of  a  gallery  behind  the  lower  portion  of  the  scarp 
wall,  the  upper  portion  being  connected  with  relieving 
arches,  so  arranged  that,  being  open  to  the  rear,  the  foot  of 
the  slope  of  earth  will  just  touch  the  back  of  the  wall  at 
its  foot  within.  In  this  exann)le,  the  pressure  of  the  earth 
being  supposed  to  be  great,  the  gallery  is  closed  in  the  rear 
by  arched  walls ;  the  arches  being  built  into  the  vertical 
piers,  B,  of  the  relieving  arches,  C.  This  example  also 
shows  the  manner  of  barricading  the  door-ways  through 
the  piers  by  vertical  grooves,  made  in  the  opposite  faces  of 
the  piers,  to  receive  the  scantling  forming  the  barricade. 

115... In  Fig.  28  is  shown  the  section  of  a  gallery  behind 
the  lower  portion  of  the  scarp,  with  the  upper  portion 
arranged  with  recesses  for  loop-holes. 

116 ...  Counterscarp  Galleries.  PI.  4,  Fig.  35.  The 
most  simple  method  of  arranging  a  gallery  behind  a  coun- 
terscarp wall,  for  the  defence  of  a  ditch,  is  to  build  another 
wall  parallel  to  that  of  the  counterscarp,  and  to  throw  an 
arch  over  between  the  two  to  cover  the  top  of  the  gallery. 
The  counterscarp  wall  is  pierced  with  loop-holes  arranged 
in  the  same  way  as  in  scarp  galleries. 

117... The  example  selected  is  from  one  of  our  works,  and 
shows  a  section  of  the  gallery  through  a  loop-hole.  A, 
counterscarp  wall;  D,  parallel  wall  ;  C,  arch  and  capping; 
JE,  glacis  mask  covering  the  scarp  wall. 

118. ..In  Figs.  29,30,  31,  are  shown  a  plan,  section  on  r  s, 
and  a  section  and  interior  elevation  on  op,  of  a  counter- 


COMPONENT    ELEMENTS    OF    PERMANENT    WORKS.  57 

scarp  gallery  taken  from  a  French  authority.  In  this  case 
counterforts,  square  in  plan,  are  built  along  the  back  of  the 
counterscarp  wall,  leaving  8  feet  between  them.  Parallel 
to  the  counterscarp  wall,  and  4  feet  in  rear  of  the  counter- 
forts, another  wall  is  built,  which,  with  the  counterforts, 
serves  as  the  support  of  a  scries  of  arches  pcr})endicular 
to  the  counterscar})  wall,  sprung  between  the  counterforts, 
and  another  parallel  to  it  and  resting  on  the  counterforts 
and  })arallel  wall.  The  arches  between  the  counterforts 
form,  with  them,  recesses,  A,  for  the  men  serving  the  loop- 
holes, pierced  in  the  counterscarp  wall ;  whilst  the  covered 
space,  B,  in  rear,  serves  for  circulation,  without  disturbing 
the  men  engaged  in  firing. 

119... Counterscarp  galleries  may  also  be  arranged  for  a 
ditch  defence  with  artillery — short  guns,  like  carronades, 
being  used  for  this  purpose.  A  plan.  Fig.  32,  a  vertical 
section  and  side  elevation  on  D  C,  Fig.  33,  and  a  section 
and  back  elevation  on  A  B,  Fig.  34,  taken  from  one  of  our 
works,  shows  a  disposition  of  this  kind  in  the  re-entering 
angle  of  the  counterscarp. 

120...Bastionnkts.  In  small  works,  where  a  flanking  dis- 
position cannot  be  obtained  from  the  enceinte,  as  in  lunettes 
and  redoubts,  the  ditches  may  be  swept  by  covered  cham- 
bers, PI.  5,  Fig.  39,  attached  to  the  scarp  wall  either  at  the 
centre  of  the  sides  of  the  work  or  at  the  angles. 

These  chambers,  PI.  5,  Fig.  39,  are  usually  of  a  pentago- 
nal form — the  sides  which  join  the  scarp  wall  serving  to 
flank  it,  and  the  two  exterior  sides,  forming  a  salient  angle, 
delivering  their  fire  on  the  opposite  counterscarp  and  its 
crest.  From  their  form  and  purposes,  they  have  received 
the  name  of  bastionnets. 

The  dimensions  of  these  constructions  will  depend  \\\)<m 
the  amount  and  kind  of  fire  to  be  delivered.  Their  scarps 
should  be  as  high  as  that  of  the  main  work.  They  com- 
municate with  the  interior  of  the  main  work,  either  directly 
b}'  galler}'  or  postern,  or  from  a  scarp  gallery. 

Fig.  39  shows  a  plan  of  a  bastionnet,  JJ,  at  an  angle  com- 
municating with  a  scarp  gailer}-,  £.     In  rear  of  the  scarp 


58  COMPONENT    KLEMENTS    Ol'    PEUMANENT    MORKP. 

gallery,  and  opposite  to  the  bastionnet,  is  placed  a  small 
powder  magazine  for  its  service.  The  exami>le  is  from 
Austrian  authority,  and  is  arranged  for  one  small  gun  on 
each  flank  besides  the  loop-holes  for  small  arms, 

121... As  a  general  rule,  it  may  be  laid  down  that  the 
salient  angles  of  the  redoubt  are  the  most  suitable  positions 
for  the  bastionnets,  as  they  will  thus  form  small  bastioned 
fronts,  in  which  both  the  sides  of  the  main  work  and  those 
of  the  bastionnet  will  be  swept  by  the  flanks  of  the  latter. 
The  only  danger  in  this  arrangement  is,  that  the  loop-holes 
in  one  flank  may  be  flred  into  from  the  opposite  one.  This, 
however,  may  be  guarded  against  by  a  suitable  })Ositiou 
given  to  the  loop-holes. 

122. ..As  the  main  object  of  covered  defences  is  protection 
against  shells,  it  is  essential  that  the  arches  of  the  galleries 
and  bastionnets  should  be  bomb-proof.  As  the  span  of 
these  arches  is  usually  small,  a  thickness  of  2  feet  given  to 
the  masonry,  and  a  covering  from  4  to  6  feet  of  earth  above 
it,  is  ordinarily  considered  sutiicient  for  tlie  object  in  view. 

123. ..With  regard  to  the  front  walls  of  these  construc- 
tions, as  tbey  are  too  thin  to  withstand  the  direct  action  of 
artillery,  they  must  either  l)e  covered  by  earthen  masks,  as 
a  glacis  raised  beyond  the  counterscarp  for  exaniplo,  or  be 
used  only  in  }K)sitions  where  they  are  nt)t  exposed  to  this 
fire. 

124. ..It  should  be  observed  that  whatever  advantages 
covered  defences  afl:brd  as  shelter  from  the  assailant's  Are, 
they  present  the  inconveniences  of  a  comparatively  narrow 
and  obstructed  fleld  of  view  to  the  assailed,  which  is  further 
obscured  by  the  smoke  which  may  gather  within  the  gal- 
lery, and  in  front  of  the  loop-holes.  From  these  causes  the 
assailed  having  to  aim  at  a  venture,  his  Arc  is  likely  to  be 
less  effective  than  in  open  defences  where  the  smoke  dis- 
perses ra})i(lly  and  leaves  a  clear  fleld  of  view.  The  same 
may  be  said  of  loop-holed  walls  covering  exterior  corridors 
where  the  space  to  the  rear  is  confined. 

Owing  to  these  considerations,  loop-holed  tnid  covered 
defences  of  the  kind   in   question  should  be  restricted  to 


COMPONENT    ELEMENTS    OF    PERxMANENT    WORKS.  59 

special  defensive  purposes,  wlicre  an  object  witliin  the  field 
of  fire  can  be  attained  with  some  certainty,  whether  seen  or 
not  by  the  assailed ;  as,  for  example,  the  protection  of  a 
ditch,  or  a  scarp  wall  which  cannot  be  flanked  from  within 
the  work  for  sweeping  a  covered-way,  or  the  interior  of  any 
outwork  which  cannot  be  lirought  well  under  the  fire  of 
the  parapet  of  the  main  work. 

125...CAP0NNIERE  Defences  for  the  Enceinte  Ditch. 
These  works  are  classed  under  the  head  of  what  are  termed 
defensive  casemates,  which  are  bomb-proof  arched  structures 
for  receiving  cannon,  which  fire  through  embrasures  pierced 
in  the  front  or  mask  w^1ll  of  the  casemates.  Defences  of 
this  class,  when  used  to  flank  the  main  ditch,  are  usually 
termed  vascmatcd  caponuieres. 

120... These  defences  are  usually  placed  in  the  main  ditch 
at  the  middle  point  of  the  side  or  front  to  be  flanked.  The 
outline  of  their  plan  is  mostly  that  of  a  lunette,  PI.  5,  Fig. 
36 — the  flanks  being  perpendicular  to  the  line  of  the  scarp, 
and  the  two  faces  making  a  salient  angle  of  60°.  The 
caponniere  is  either  built  in  juxtaposition  with  the  en- 
ceinte, or  else  detached  from  it.  In  the  latter  case,  an  enclo- 
sure is  formed  between  the  two  by  a  loop-holed  wall  which 
connects  the  flanks  with  the  scarp  wall.  Each  flank  con- 
sists of  one  or  two  tiers  of  arched  chambers  —  the  piers  of 
the  arches  being  perpendicular  to  the  back  of  the  walls  of 
the  flank.  p]ach  chamber  is  of  sufficient  dimensions  for  the 
service  of  a  single  gun  with  a  contracted  field  of  fire,  PI.  5, 
Figs.  36,  37.  In  some  cases,  loop-holes  are  [>icrced  for  small 
arms  on  each  side  of  the  embrasure ;  in  others,  the  case- 
mates of  one  story  are  pierced  for  cannon  and  the  other  for 
small  arms. 

127. ..The  casemates  are  closed  in  rear  by  a  thin  wall, 
Avhich  is  provided  with  windows  for  light  and  ventilation  ; 
and  the  piers  are  pierced  with  door-wa\s,  to  form  a  commu- 
nication between  the  chambers  and  to  assist  the  ventilation. 
Flues  or  vents,  Fig.  37,  are  made  in  the  front  wall,  just 
under  the  arches,  for  a  like  purpose.  Where  it  may  be 
necessary,  the  lower  floor  is  drained  by  a  conduit  through 
the  front  wall. 


60  COMPONENT    KLEMKNTS    OF    PERMANENT    WORKS. 

128. ..All  open  court  is  left  between  tlie  flanks,  and  each 
flank  is  covered  at  top  with  from  4  to  6  feet  of  earth.  The 
flanks  are  sejiaratcd  from  the  faces  by  a  closed  corridor, 
which  serves  as  a  communication. 

129... In  front  of  the  corridor  and  on  each  side  of  the 
axis  of  the  caponniere,  a  caseniated  chanil)er,  which  is  open 
in  front,  is  arranged  for  one  mortar,  Figs.  36,  38.  The 
arches  of  these  chambers  rise  toward  the  front,  tlie  better  to 
subserve  the  object  in  view. 

130... On  one  side  of  tlie  chambers  tlie  pow^der  magazine 
is  placed,  with  a  store-room.  On  the  other  side  a  stair-waj 
between  the  stories  is  built. 

131... The  space  within  the  salient  angle,  enclosed  by  the 
walls  of  the  faces  and  the  front  of  the  mortar  casemates,  is 
open  at  top.  It  has  an  open  corridor  for  communication, 
and  the  front  walls  are  arranged  with  loop-holed  recesses 
for  small  arms.  Figs.  36,  38. 

132. ..The  enceinte,  in  rear  of  the  flanks  of  the  cajionniere, 
is  arranged  with  a  scarp  gallery,  to  flank  the  cai)oiiniere 
flanks  and  the  court  between  them.  A  lireak  is,  in  some 
cases,  made  in  the  lino  of  the  scarp  wall,  })eri)endieular  to 
the  caponniere  faces,  and  casemates  for  cannon  and  small 
arms  arranged  behind  the  scarp  wall  to  flank  these  faces. 
In  some  cases  these  flanking  dispositions  are  placed  in  front 
of  the  scarp  wall,  the  casemates  being  open  to  the  rear, 
looking  on  a  narrow  court  between  them  and  the  scarp 
which  is  closed  on  the  sides  bj'  a  loop-holed  wall. 

133..  The  example  here  given  of  a  caseniated  caponnitire 
is  from  an  Austrian  authority.  Fig.  30  is  the  i)lan  ;  F'ig. 
37  a  scelion  and  elevation  on  A  B  of  one  Hank  and  the  end 
wall  of  the  corridor  looking  toward  the  court  between  the 
flanks  ;  Fig.  38  a  section  and  elevation  along  CD'  of  the 
corridor,  mortar  casemate  and  triangular  court;  Figs.  37,  38, 
are  on  an  enlarged  scale. 

134. ..Casemates  on  Land  Fronts.  Various  modes  have, 
from  time  to  time,  been  proposed  for  arranging  defensive 
casemates  for  the  exterior  defence  on  land  fronts.  'J'he 
diflieulty  in  covering  the  masonry  from  the  batteries  of  the 


COMPONENT    ELEMENTS    OF    PERMANENT    WORKS.  Gl 

assailant  lias  heen  the  chief  ohjcction  to  these  structures, 
and  is  the  more  pronii*nent  as  the  tire  of  artillery  hecomes 
more  accurate,  as  such  casemates  Avould  soon  l)e  rirnu'd 
or  rendered  untenahle  by  embrasure  shots. 

135. ..The  structure  for  this  purpose  which  has  been  most 
applied  within  late  j^ears,  is  what  is  termed  the  Haxo  case- 
mate;  the  details  having  been  first  proposed  by  General 
Haxo,  one  of  the  first  authorities  of  the  French  school  of 
engineers.  These  casemates  consist,  Figs.  45,  46,  47,  of  a 
series  of  arched  bomb-proof  chambers,  closed  in  front  by 
a  thin  mask  wall,  which,  except  around  the  embrasures 
through  it,  is  covered  from  the  assailant's  artillerj^  by  the 
parapet.  To  present  but  a  small  surface  of  masonry  to 
fire,  the  arches,  which  are  horizontal  and  perpendicular 
to  the  mask  wall  f(3r  the  greater  portion  of  their  length, 
descend  toward  the  front,  leaving,  where  they  join  the 
mask  Avail,  just  sufficient  height  within  for  the  service  of 
the  gun.  To  effect  this,  the  anterior  portion  of  the  arch 
must  be  conoidal  in  shape. 

136... The  piers  of  the  arches  are  pierced  with  wide 
arched  openings,  which  serve  the  double  purpose  of  a  com- 
munication between  the  casemates  and  to  give  the  gun 
a  wider  traverse  for  firing. 

137... Embrasures  are  pierced  in  the  parapet  in  prolon- 
gation of  those  of  the  nuisk  wall,  and  it  is  proposed  to 
cover  the  small  portion  of  the  masonry  necessarily  exposed 
by  this  arrangement,  by  placing  several  thicknesses  of 
heavy  timber  in  front  of  it  to   receive  the  shot. 

188... When  the  casemates  serve  simply  for  the  cover  of 
the  cannon,  the  arches  are  covered  with  from  4  to  6  feet 
thickness  of  earth,  and  are  left  open  to  the  rear  for  the 
more  prompt  escape  of  the  smoke,  and  a  ditch  is  sometimes 
made  just  in  rear  of  the  casemates  to  catch  bombs  and  limit 
the  effects  of  their  explosion.  When  the  arches  are  made 
longer  than  for  the  service  of  the  guns  alone,  the  earthen 
covering  is  sometimes  arranged  with  a  parapet  to  cover 
cannon  in  harhette,  or  for  small  arms. 

139. ..The  examples  shown  bv  the  Figures  is  from  a  French 


62  COMPONENT    ELEMENTS    OF    PERMANENT    WORKS. 

authority.  Fiij.  45  is  a  plan  on  vi  ??,  Fig.  47 ;  Fig.  4G  a 
section  and  interior  elevation  toward  the  mask  wall  on  op, 
Fig.  47;  and  Fig.  47  a  section  and  side  elevation  on  rs, 
Figs.  45,  4G. 

140. ..In  Figs.  48,  40,  is  shown  an  arrangement  of  two 
casemates  of  the  liaxo  kind,  from  an  Austrian  authority. 
In  this  case,  the  masonry  is  covered  on  the  flanks  from 
enfilading  fire  l)y  earth.  Fig.  48  is  an  interior  elevation  of 
the  arches,  and  the  hack  wall  that  retains  the  earth  on  the 
sides.  Fig.  49  is  a  longitudinal  section,  and  sliowa  the 
manner  of  covering  the  masonry  in  front  and  securing  the 
earthen  emhrasure  by  a  timber  facing. 

141. ..Mortar  Casemates.  In  Fig.  50,  PI.  6,  is  shown  a 
longitudinal  section  of  a  mortar  casemate  placed  in  rear  ot 
a  parapet,  by  wdiich  it  is  covered  from  direct  fire.  The 
arch  is  covered,  as  in  the  preceding  case,  bv  earth,  to  break 
tlie  shock  of  shells.  It  rises  toward  the  front,  to  give 
ample  room  for  the  shell  in  its  flight.  The  casemates  are 
covered  on  their  flanks  from  enfllading  Are  by  an  embank- 
ment, and  are  i)artly  closed  by  a  wall  in  rear.  A  small 
ditch  is  made  in  front  of  the  chamber,  and  a  slight  wall 
built  wnthin  it,  to  give  cover  from  the  splinters  of  shells 
falling  between  the  parapet  and  casemate.  Arched  cham- 
bers are,  in  some  cases,  made  beneath  the  mortar  chamber, 
which  serve  as  store-rooms  and  temporary  magazines. 

142. ..When  these  casemates  are  placed  in  rear  of  a  por- 
tion of  the  parapet,  Ijut  little  exposed  to  direct  Are,  the 
thickness  of  the  parajjct  in  front  of  them  may  l)e  reduced, 
and  the  interior  slo})C  be  replaced  by  a  breast-height  wall 
along  the  front  of  the  casemates,  in  order  to  give  bi-tter 
cover  in  flank  and  from  slant  Are,  by  throwing  forward  the 
casemates  more  under  cover  of  the  parapet. 

143. ..The  example  given  is  from  the  same  authority  as  in 
the  preceding  example  of  casemated  caponnicres. 

144... Casemates  for  Water  Fronts.  In  the  casemated 
batteries  for  sea-coast  and  harbor  defence,  the  scarp  or 
mask  wall  of  the  chambers  for  the  guns,  being  exposed  to 
the  fire  of  ships  alone,  are  not  covered,  as  on  land  fronts, 


COMPONENT    ELEMENTS    OF    PERMANENT    AVORKS.  63 

by  an  earthen  mask;  these  walls  being  built  of  sufficient 
thickness  and  strength  to  withstand  the  fire  of  the  lieaviest 
guns  within  the  range  that  ships  can  venture  to  attack,  and 
being  far  less  vulnerable  than  the  wooden  or  iron  sides  of 
vessels* thus  far  brought  into  general  use. 

145. ..These  batteries,  in  our  own  and  European  works, 
consist  of  a  series  of  arched  bomb-proof  chambers,  which 
serve  for  the  service  of  the  guns  alone;  or  else  thev  receive 
such  dimensions  that  the  portions  of  the  chambers  imme- 
diately in  rear  of  the  mask  wall  are  appropriated  to  the 
service  of  the  battery,  and  the  rear  portions  are  converted 
into  quarters,  store-rooms,  and  other  necessary  purposes  for 
the  garrison. 

14G...In  the  earlier  sea-coast  casemated  defences  con- 
structed in  our  service,  the  gun  chambers  have  received 
dimensions  to  admit  of  two  guns  in  each  chamber,  PI.  5, 
Figs.  40,  41.  The  chaml)ers  are  usually  formed  of  seg- 
mental brick  arches  of  120°,  which  rest  upon  stone  piers 
built  back  perpendicular  to  the  mask  wall.  In  the  example 
given,  the  arches,  C,  have  a  uniform  thickness  of  3  feet, 
exclusive  of  the  roof-shaped  capping,  which  is  generally  of 
rubble  and  beton,  and  which  is  covered  on  top  by  the  earth 
of  the  parapet  and  rampart.  The  stone  piers,  jB,  are  6J  feet 
thick,  and  are  pierced  with  arched  communications,  F^  a 
few  feet  in  rear  of  the  mask  wall,  so  placed  as  to  give  tlie 
gun-carriage  a  wider  traverse  b}^  allowing  it  to  run  under 
this  oj)ening.  Arched  recesses,  E,  are  made  in  the  mask 
wall  to  admit  the  muzzle  of  the  gun  being  well  run  out,  so 
as  to  clear  the  cascnnite  of  smoke.  An  embrasure,  f,  is 
pierced  at  the  centre  of  each  recess,  the  sole  being  at  the 
proper  height  above  the  floor  of  the  casemate,  to  accommo- 
date the  casemate  chassis  and  top  carriage.  In  Fig.  40,  is 
sliown  the  plan  and  dimensions  of  the  embrasures  usually 
adopted  in  our  works,  until  a  very  recent  date;  and  in  Fig. 
41,  which  is  a  vertical  section  of  the  casemate  through  the 
axis  of  an  embrasure,  is  shown  the  elevation  and  dimen- 
sions of  the  cheeks,  c,  of  the  embrasure.  In  the  casemates 
of  some  of  our  works,  flues  for  veutihition  and  carrying  ofl:' 


64  COMPONENT   ELEMENTS    OF    PERMANENT    WORKS. 

rapidly  tlie  powder  smoke,  run  from  the  top  of  the  carriage 
recesses,  E,  through  the  masonry  of  the  scarp  wall,  and 
have  their  outlet  in  the  tf)p  of  the  wall.  In  others,  tlie 
flues  rmi  fi-oni  the  casemate  arcli  to  the  top  of  tlie  itarapet. 
Beneath  the  emhrasure  a  recess,  termed  the  (oiii/nc-holc, 
which  in  plan  is  triangular,  is  made  to  receive  the  tongue 
of  the  chassis.  The  tongue  is  contined  in  its  place,  and  the 
chassis  traverses  around  a  pintle  which  is  received  into  the 
jyinilc-hole,  made  at  the  centre  point  of  the  throat  of  the 
embrasure,  and  extending  into  the  masonry  Ix'low  the 
tontjue-hole. 

147... When  the  casemates  serve  also  as  quarters  for  the 
garrison,  the  rear,  toward  the  parade,  is  closed  by  a  brick 
or  stone  parade  wall,  which  forms  the  front  wall  of  the 
quarters.  A  brick  i)artition  wall  separates  the  quarters 
l"r(>m  the  gun  gallery.  Arched  recesses  and  flues  are  made 
in  the  piers  for  chimneys;  and  the  jyarade  wall,  the  sides  of 
the  piers,  and  soflit  of  the  arch,  are  suitably  finished  to  give 
a  dry  and  well-ventilated  dwelling. 

148. ..In  the  example  here  given,  as  in  most  of  our  earlier 
casemated  works,  there  is  but  one  tier  of  casemated  guns ; 
this  tier  being  surmounted  by  a  barbette  batter}*,  covered 
either  by  an  earthen  or  stone  parapet  on  the  water  fronts. 

149... Casemates  adapted  to  two  guns  in  each  room, 
present  a  more  vulnerable  mark  in  the  portion  of  the 
mask  wall  between  the  piers;  ex}iose  more  men  to  danger 
from  embrasure  shots;  }»resent  a  greater  opening,  in  rear, 
to  the  assailant's  Are,  when  not  closed  by  a  parade  wall; 
ofter  less  resistance  to  the  shock  of  shells,  and  are  more 
difficult  to  construct,  without  settling,  than  rooms  for 
single  guns.  These  advantages  in  favor  of  casemates  for 
single  guns  are  the  more  marked  where,  for  the  purpose  of 
obtaining  a  heavy  fire  in  some  fixed  direction,  it  is  desirable 
to  resort  to  a  castellated  structure,  consisting  of  several  tiers 
of  casemates. 

150... In  PI.  6,  Figs.  42,  43,  44,  is  shown  a  plan,  Fig.  42, 
on  E  F,  of  the  first  tier  of  casemates;  a  vertical  section 
and   side  elevation,  Fig.  43,  on  A  B,  of  the  three  tiers  of 


COMPONENT    ELEMENTS    OF    PERMANENT    WORKS.  65 

casemates  and  the  top  l)arbette  battery;  and,  in  Fio;.  44,  an 
interior  deviation  on  C  D^  of  one  of  the  most  recent  of 
these  structures  for  the  defence  of  the  channel  leading  to 
one  of  our  harbors.  Besides  the  wide  arched  openings,  F^ 
through  the  piers,  for  communication  and  the  traverse  of 
the  guns,  snuiller  door-ways,  «,  are  made  for  communications 
in  rear  of  the  battery.  The  casemates  are  open  in  the  rear. 
The  arches  of  the  top  tier  are  alone  made  bomb-proof; 
those  of  the  lower  tiers  receiving  sufficient  strength  to 
receive  the  armament  and  admit  of  the  service  of  the 
guns  with  safety. 

151...E3n5RASURES.  The  form,  dimensions  and  construc- 
tion of  embrasures  in  mask  walls,  present  a  problem  which 
lias  offered  no  little  difficulty,  in  a  satisfactory  solution,  to 
engineers,  by  which  the  best  cover  could  be  given  to  the 
guns  and  men,  by  exposing  the  least  surface  to  embrasure 
shots,  whilst  the  guns  should  receive  a  suitable  traverse  to 
command  a  wide  field  of  fire. 

152. ..In  the  embrasures  of  our  works,  the  general  form 
is  the  same  as  those  usually  found  in  Europe,  but  they 
present  a  very  considerable  less  amount  of  exterior  and 
throat-opening  than  European  embrasures.  See  PI.  7, 
Fig.  59,  which  is  the  plan  of  a  French  carriage  recess  and 
embrasure  for  a  single  gun,  and  Fig.  60,  which  is  one  of 
the  same  parts  of  an  p]nglish  fort  for  sea-coast  defence. 
In  some  of  our  earlier  works,  the  sole,  cheeks  and  top 
(»f  the  embrasures  are  constructed  of  brick,  as  being  a 
material  that  would  be  less  destructive  throutrh  the 
splinters  driven  in  by  embrasure  shots.  This  view,  how- 
ever, lias  been  abandoned  in  our  more  recent  works,  the 
embrasures  being  constructed,  on  the  contrary,  of  heavy 
stone  blocks,  carefully  and  strongly  bonded;  a  brick  arch 
being  thrown  above  the  enibrastire,  within  the  mass  of  the 
mask  wall,  to  secure  the  up[ter  portion  from  yielding 
should  the  block  forming  the  ceiling  of  the  embrasure  be 
damaged. 

15v5...A  further  and  most  importaiit  ste[i  has  been  more 
recently  taken,  in  the  application  to  embrasures  of  wrought- 
5 


66  COMPONENT    ELEMENT?    OF    PERMANENT   WORKS. 

iron  casings  and  tliroat-pieees.  Avitli  shutters  of  tlie  same 
material,  as  a  security  against  heavy  shot  and  grape.  The 
first  application  of  this  means  lias  been  made  to  the  em- 
brasures of  one  of  our  works  now  in  the  course  of  con- 
struction; and  the  forms,  dimensions  and  construction  of 
the  embrasures  arc  the  results  of  experiments  carefully 
made  with  the  heaviest  solid  shot  and  grape,  u}Hm  walls 
and  embrasures  of  various  forms  and  dimensions,  under 
the  directions  of  General  Totten,  chief  engineer. 

1 0-1. ..The  form  adojjted  is  shown  in  plan  in  PI.  8,  Fig. 
01 — the  interior  portion  being  trapezoidal,  and  the  exterior, 
beyond  the  throat,  rectangular.  This  form  was  adopted 
with  the  double  view  of  limiting  the  effects  of  embrasure 
shot  which,  in  the  old  forms,  striking  the  oblique  surfaces 
of  the  cheeks  of  the  exterior  portion  and  glancing  inward, 
occasioned  considerable  casualties,  and  to  form  a  suitable 
recess  for  strong  iron  shutters  to  protect  from  grape  enter- 
ing through  the  throat  whilst  the  gun  was  out  of  battery. 
The  two  principal  wrought-iron  throat-pieces  are  trape- 
zoidal in  plan,  l)eing  <S  inches  thick  and  17  inches  base, 
the  oblique  side  having  the  same  slant  as  tlie  inner  cheek 
of  the  embrasure.  Exterior  to  these  two  })ie{'es  are  two 
plate-pieces,  each  two  inches  thick,  against  wirK-h  the 
shutters,  which  are  also  tAvo  inches  thick,  rest  when  open 
or  closed,  as  shown  in  Fig.  01,  There  is  also  a  wrought- 
iron  plate  casing  around  the  exterior  opening  of  the 
embrasure,  as  shown  in  Fig.  61,  and  in  the  exterior  eleva- 
tion. Fig.  64.  In  Fig.  62  is  shown  an  interi(M*  elevation  of 
the  carriage  recess,  tlie  embrasure,  and  the  tongue-hole ; 
and,  in  Fig.  63,  a  vertical  section  and  side  elevation  on 
A  B,  Fig.  64,  of  the  embrasure,  carriage  recess,  and  the 
])intle  and  tongue-holes. 

lor)...The  exterior  width  of  the  embrasure,  the  obliquity 
given  to  the  cheeks  of  the  interior  portion,  and  tlie  depth 
and  slant  given  to  the  carriage  recess  and  its  sides,  are 
arranged  with  a  view^  to  the  traverse  of  the  gun,  which  is 
fixed  at  60°,  or  30°  on  each  side  of  the  axis  of  the  em- 
brasure. 


COMPONENT    ELEMENTS    OF    PERMANENT    WORKS.  G7 

156... All  the  parts  of  the  wall  adjacent  to  the  embrasure 
are  constructed  of  the  largest  sized  Ijlocks  of  the  toughest 
stone,  the  blocks  being  carefully  fitted  and  bonded,  and 
having  the  additional  strength  afforded  by  a  very  ingenious 
arrangement  of  hollow  bolts,  and  a  concrete  of  lead  and 
chippings  of  stone  run  together.  A  brick  arch,  as  sliown  in 
the  elevations  and  sections,  is  turned  over  the  embrasure  and 
within  the  mass  of  the  scarp  wall. 

157. ..Bomb-proof  Buildings.  Casemated  bomb  })roof 
quarters  are  indispensable  to  the  safety  and  comfort  of  the 
garrison  during  siege,  or  any  prolonged  attack  for  the  annoy- 
ance or  reduction  of  the  work  by  a  bombardment.  lu  small 
works  like  the  most  of  our  forts,  which  are  chiefly  designed 
for  sea-coast  defence,  casemated  quarters  are  arranged  as  has 
been  seen  in  the  rear  of  the  batteries,  a  portion  of  each 
casemate  toward  the  parade  being  partitioned  off  and  suit- 
al)ly  disposed  for  the  olycct  in  view.  In  some  cases  advan- 
tage is  taken  of  a  scai'p.wall,  on  a  land  front,  which  is  well 
covered  b}-  a  glacis  or  other  face  cover,  to  form  in  its  rear 
quarters  of  this  character.  In  all  cases,  care  should  be 
taken  to  place  such  quarters  on  those  fronts  which  are  best 
covered  from  a  direct  fire,  and  the  parade  walls  of  which 
are  not  exposed  to  reverse  fire.  Whenever  the  plan  of  the 
work  admits  of  it,  quarters  of  this  kind  should  be  arranged 
for  defence,  by  being  pierced  with  loop-holes,  and  even  with 
embrasures  for  cannon.  Defensive  casemated  quarters  form 
a  prominent  and  distinctive  feature  in  what  is  now  known 
as  the  German  school  of  permanent  fortification.  They 
consist  of  bomb-[>roof  buildings  of  a  curvilinear  or  poly- 
gonal plan,  arranged  for  one  or  more  stories  of  covered 
defences,  with  an  ordinary  open  defence  surmounting  the 
casemates.  The  casemates  of  the  upper  story  are  covered 
by  boml)-proof  arches,  whilst  those  of  the  lower  stories 
receive  fiat  segment  arches  of  only  sufficient  thickness  and 
strength  to  bear  the  weiglit  of  the  guns  and  to  subserve  the 
other  objects  of  the  structure.  When  employed  as  capon- 
nieres,  as  gorge  defences,  or  as  interior  retrenchments,  tlie 
front  walls  of  tliese  structures  are  masked  from  direct  view.s, 


08  COMPONENT    ELEMENTS    OF    PERMANENT    WORKS. 

eitlier  b}-  the  glacis  or  by  the  i)araj)Ot  of  tlio  work  in  wliioli 
they  are  placed,  and  they  receive  a  tliickness  of  at  least  5 
feet.  But  as  a  mask  wall  even  of  this  tliickness,  when 
pierced  with  loop-holes  and  embrasures,  is  liable  to  damage 
from  shot  which  plunge  over  the  parapet  in  front  of  it,  PI. 
7,  Fig.  53,  the  portions  of  the  casemate  piers,  B,  where  they 
join  the  mask  w-all,  A,  are  made  thicker,  in  some  cases  for 
a  distance  of  a  few  feet  back,  than  their  general  thickness, 
in  order  to  receive  two  vertical  grooves  in  the  face  of  this 
thicker  portion,  into  which  scantling  being  inserted  liori- 
zontally,  and  tlie  space  between  the  two  partitions  tluis 
formed  tilled  in  with  sand-bags  or  other  shot-proof  mate- 
rials, a  temporary  shelter  can  be  formed  when  the  ruin  of 
the  mask  wall  exposes  tlie  interior  of  the  casemate  to  view. 

In  our  service,  PI.  7,  Figs.  51,  52,  when  casemated  quar- 
ters are  constructed  of  two  stories,  the  upper  one  alone  is 
covered  with  a  bomb-proof  arch,  the  floor  between  the  two 
being  of  timber,  and  constructed  in  the  ordinary  way. 

158. ..In  Fig.  51  is  shown  a  plan  on  A  D,  Fig.  52,  of  bomb- 
proof casemated  quarters  in  rear  of  a  scarp  wall  and  of  a 
counterscarp  gallery,  both  arranged  with  loop-holed  de- 
fences. Fig.  52  is  a  section  and  side  elevatioh  on  CD,  Fig. 
51,  sliowing  the  i-ain})art  and  parapet  over  the  arch  and  the 
fireplaces  and  chimneys  in  the  piers  of  the  arches.  The  floor 
of  the  second  story  is  of  timber.  The  rear  or  parade  wall 
is  pierced  with  doors  and  windows. 

159. ..In  Fig.  53  is  shown  the  plan  of  the  end  of  a  case- 
mated  defensive  barrack,  from  an  Austrian  authority.  The 
front  wall.  A,  is  arranged  and  pierced  for  cannon,  each  arched 
chamber  for  one  gun.  The  end  wall  is  loop-holed  for  mus- 
ketry, and  the  rear  wall,  C,  has  windows  and  doors. 

IGO... Powder  Ma(jazine.  The  structures  for  this  purpose 
are  built  with  strong,  full  centre,  bomb-proof  brick  arches, 
8U[)portcd  on  heavy  stone  piers,  which  form  the  outward 
walls  and  to  which  interior  buttresses  are  sometimes  added. 
The  capping  of  the  arches  is  covered  with  fi-om  4  to  fi  feet 
of  solidly  i)acked  earth.  The  interior  of  the  magazine,  the 
floors,  and  the  doors  and  windows,  are  built  with  a  view  to 


COMPONENT    ELEMENTS    OF    PERMANENT    WORKS.  69 

security  from  fire;  and  to  preserve  the  powder  from  damp- 
ness, by  a  good  system  of  drainage  around  the  foundations, 
and  of  ventilation  by  means  of  air-holes  made  through  the 
piers,  and  panels  of  copper  pierced  with  small  holes  placed 
in  the  doors.  No  iron  or  steel  fastening  or  sheeting  is 
allowed  in  any  part  of  the  structure  ;  and  in  arranging  the 
air-holes  through  the  piers,  they  receive  a  broken  direction 
and  have  a  copper  mesh-work  [)laccd  across  them,  to  pre- 
vent any  combustible  material,  or  rats,  or  mice,  penetrating 
to  the  interior  of  the  magazine. 

In  large  works  the  magazines  are  isolated,  as  far  as  prac- 
ticable, from  the  enceinte,  so  as  not  to  endanger  it  should 
an  accidental  explosion  take  place.  The  magazine  is  en- 
closed by  a  strong  high  wall  for  security,  and  is  provided 
wnth  lightning-rods.  In  small  works  some  one  or  more  of 
the  casemates,  in  the  least  exposed  position  to  the  assail- 
ant's fire,  is  built  for  the  purposes  of  a  magazine. 


COMMUNICATIONS. 

161. ..The  communications  form  a  very  important  ele- 
ment in  the  defence  of  permanent  works.  They  consist  of 
ramps,  stairs,  posterns,  gate-xrays  and  bridges. 

162... K AMPS.  Ramps  are  inclined  planes,  or  paths,  lead- 
ing from  one  level  to  another,  as  from  that  of  the  parade 
to  the  terrei)lcin  of  the  enceinte.  Their  width  at  top,  for 
the  service  of  the  artillery  and  other  vehicles,  maj*  be  from 
10  to  15  feet,  and  their  inclination  from  \  to  ,'5,  or  less, 
depending  on  the  difference  of  level  to  be  overcome.  Tbey 
are  usually  placed  in  positions  where  tbey  will  occupy  the 
least  room  of  the  parade  —  as  along  the  rampart-slope  of 
the  enceinte.  As  a  general  rule,  their  side-slopes  are  of 
earth  ;  but  where  it  is  desirable  to  economise  room  on  the 
parade,  the  side-slopes  are  replaced  on  one  or  both  sides  by 
a  wall  which  sustains  the  earth  of  the  ramp.  When  ramps 
serve  for  infantry  alone,  their  width  may  be  reduced  to  6 
feet,  and  in  some  cases  to  4  feet. 


70  COMPOXEXT    ELEMENTS    OF    PERMAXKXT    WORKS. 

163... Stairs.  Stairs,  except  for  teniporarv  purposes,  are 
constructed  of  stone;  eacli  step  boint^  a  solid  block  Avbicli 
is  0  feet  long  in  tlie  clear;  its  breadtli  at  top  or  tbc  tread 
12  inches,  and  its  height  or  rise  8  inches.  Stairs  arc  usually 
placed  along  the  counterscai-p  and  gorge  walls  of  the  out- 
works, forming  a  communication,  for  infontry  only,  be- 
tween the  ditch  and  the  tcrreplein  of  the  work  to  which 
they  lead.  They  are  also  used  wntliin  the  enceinte  in 
positions  where  there  is  not  sufficient  room  for  ramps  ;  or 
where,  for  greater  security  from  surprise,  it  is  desirable  to 
present  a  narrower  and  more  difficult  defile  to  the  assail- 
ant. In  cases  where  room  is  wanting  and  the  communi- 
cation not  in  hal)itual  use,  the  width  of  the  stairway  may 
be  reduced  to  4  feet. 

164...PosTERXS.  Posterns  are  arched  passageways  con- 
structed under  the  terrepleins  and  ramparts,  forming  sub- 
terranean communications  between  the  parade  and  the 
enceinte  ditch,  or  between  the  ditches  and  the  interior  of 
the  outworks.  The  w-idth  and  height  of  the  interior  of 
posterns  depend  upon  the  use  to  which  the  communication 
is  to  be  applied.  For  artillery,  the  width  is  usually  taken 
at  10  feet,  and  the  height  under  the  crown  or  key  of  the 
arch  at  least  8  feet.  Posterns  for  infantry  may  be  only 
from  0  to  4  feet  wide,  and  from  G  feet  6  inches  to  8  feet 
hiffh  under  the  crown  of  the  arch.  The  thickness  of  the 
piers  of  the  arches  is  generally  taken  at  about  half  the 
width  of  the  postern.  The  arches  arc  from  18  inches  to  2 
feet  thick.  As  any  injury  to  the  arch  from  the  bursting  of 
a  shell  over  it  might  obstruct  the  communication,  the  arch 
should  be  covered  with  a  thickness  of  at  least  3  feet  of 
earth,  and,  when  convenient,  with  5  or  6  feet  for  greater 
security.  A  strong  wooden  door  is  placed  at  each  outlet 
of  the  postern  to  secure  it  against  surprise.  The  door-way 
in  posterns  for  the  service  of  artillery  should  be  of  just 
sufficient  lieight  for  the  convenient  passage  of  a  gun  — 
about  7  feet  for  each  dimension  is  usually  allowed  for  this 
purpose. 

165. ..The  most  important  postern  is  the  one  leading  from 


COMPONENT    ELEMENTS    OF    PERMANENT    WORKS.  71 

the  parade  to  the  enceinte  ditch.  This  generally  receives 
a  width  of  12  feet,  and  the  same  height  under  the  crown. 
For  greater  security  from  surprise,  its  outlet  at  the  enceinte 
ditch  is  at  least  6  feet  above  the  bottom  of  the  ditch  — 
this  difference  of  level  being  overcome  by  means  of  a  tem- 
porary wooden  ramp,  which  receives  an  inclitiation  of  at 
least  ^.  With  a  like  object,  besides  two  strong  doors  at 
the  two  ends  of  the  postern,  there  is  a  partition  of  masonry 
about  midway  between  the  two  ends,  which  is  pierced  with 
a  door-way  of  the  same  size  as  the  door-ways  of  the  ends, 
and  closed  by  a  strong  door  which,  as  well  as  the  partition 
wall,  is  loop-lioled  f<n*  musketry. 

1(36. ..In  cases  where  the  postern  forms  the  main  entrance 
to  the  work,  an  arched  chamber  is  placed  on  one  side  of  it, 
at  the  outlet,  which  serves  as  a  guard-room  for  a  few  men, 
to  secure  the  outlet  from  surjirisc.  The  wall  between  this 
chamber  and  the  postern  is  loop-holed,  so  that  a  tire  can 
be  brought  to  bear  on  the  door-waj'  of  the  postern  ;  and,  as 
a  farther  precaution  against  surprise,  a  machicoulis  defence 
is  sometimes  arranged  at  the  top  of  the  scarp  wall  just 
above  the  door-way  of  the  postern. 

1(>7...(tate-way.  In  works  with  large  garrisons,  where 
the  means  of  frequent  communication  with  the  exterior 
are  requisite,  posterns  of  tlie  oi'dinary  dimensions  are  found 
not  to  afford  a  sufficient  convenience  for  the  daily  wants. 
In  such  cases  a  passageway  of  sufficient  width  to  admit  of 
at  least  a  single  carriage  road,  with  narrow  foot-])aths  on 
each  side,  has  to  be  opened  through  the  rampart,  which, 
whenever  it  is  practicable  to  do  so,  shouhl  be  arched,  and 
covered  with  earth  to  render  it  bomb-proof  This  j)assage- 
wa^'  should,  for  security,  have  the  bottom  of  its  outlet  at 
least  12  feet  above  tlic  bottom  of  the  enceinte  ditch  ;  and 
when  this  difference  of  level  cannot  lie  obtained,  the  maiji 
ditch  should  be  deepened  sufficiently  lor  the  purpose  below 
the  outlet.  A  gate-way  of  sufficient  height  and  width  lor 
the  passage  of  the  ordinary  vehicles  for  the  service  of  the 
garrison  is  made  through  the  scarp  wall.  This  gate-way  is 
aiched  at  top,  where  a  niacliicoulis  defence  may  also  be 
arranirod  to  iruard  the  outlet  on  the  exterior. 


72  COMPONENT    ELEMENTS    OF    PERMANENT    WORKS. 

168. ..The  communication  across  tlic  enceinte  ditch,  lead- 
ing from  the  gate-way,  is  usually  an  ordinary  wooden  bridge 
built  on  piles.  The  bay  of  this  bridge  at  the  gate-way  is 
spanned  by  a  drawbridge  of  timber,  whirli,  when  drawn 
up,  closes  and  secures  the  gate-way.  This  drawbridge  is 
manoeuvred  by  some  of  the  usual  mechanisms  employed 
for  this  purpose, 

169... Portcullis,  AVhen  the  gate-way  is  not  preceded 
by  a  ditch,  and  is,  therefore,  without  a  drawbridge,  a  bar- 
rier, termed  a  portadlis,  which  can  be  lowered  or  raised 
vertically  by  machinery,  is  sometimes  added  to  secure  the 
l^assageway  from  surprise.  The  ancient  portcullis  was  a 
framework  of  heavy  beams,  placed  vertically,  leaving  a 
few  inches  only  between  each  pair  of  beams.  These  verti- 
cal beams  were  either  solidly  confined  between  horizontal 
beams,  or  clamping-pieces  in  pairs;  or  else  they  were  so 
arranged  that  they  could  slide  upward  between  the  clamp- 
ing-pieces. Each  of  the  vertical  beams  was  shod  at  the 
bottom  with  a  strong  pointed  iron  shoe.  Tlie  horizontal 
pieces  were  framed  securely  with  two  heavy  vertical  beams 
that  formed  the  sides  of  the  frame,  and  were  fitted  into 
vertical  grooves  made  in  tlie  side  walls  of  the  passageway, 
in  which  the  iVanie  could  slide  when  raised  or  lowered. 
By  arranging  the  vertical  beams  to  slide  upward  between 
the  claniping-])ieces,  it  will  enable  the  passageway  to  be 
closed  ill  })laces  where  an  obstruction  might  be  designedly 
placed  l)elow  the  portcullis  to  })revent  this  being  done;  as 
the  beams  which  meet  the  obstruction  would  be  pushed 
upward,  whilst  the  others  would  fall  to  their  ordinary  level 
and  close  the  passageway  on  each  side  of  the  obstruction. 

170. ..In  the  works  recently  constructed  with  us,  the 
portcullis,  and  even  the  doors  preceding  them,  have  been 
constructed  of  a  strong  open  lattice-work  of  wrought-iron 
bars  bolted  strongly  to  the  wrought-iron  uprights  and  cross 
pieces  forming  the  framewf)rk  of  the  lattice.  This  is  a 
great  improvement  for  these  purposes,  both  as  to  durability 
and  defence. 

171. ..Passageways  of  this  description  should  be  secured 


ELEMENTS  OF  THE  PLAN  OF  ENCEINTES  AND  OUTWORKS.       73 

b}'  all  the  moans  at  an  engineer's  disposal.  A  large  guard- 
room, with  loop-holes  bearing  on  the  passage,  should  be 
erected  on  one  side,  near  the  gate-way;  and  it"  the  enceinte 
is  a  simple  one,  without  outworks  beyond  its  ditch,  a  small 
lunette,  or  a  loop-holed  tambour  of  masonry  or  timber, 
should  be  constructed  beyond  the  counterscarp,  forming  a 
tete-de-pont,  for  the  security  of  the  bridge  from  surprise. 

172. ..The  drawbridge,  which  for  convenience  of  manoeu- 
vring should  not  be  longer  than  12  feet,  is  constructed  in 
the  usual  mode.  Care  sliould  be  taken  that  it  shall  fit  the 
recess  in  the  face  of  the  wall  so  closely  that  there  will  not 
be  room  enough  between  it  and  the  jambs  of  the  gate-way 
to  insert  an  iron  lever  to  force  back  the  bridge. 


OMciucntfi  of;  the  |31;in  of:  dinccinfcfi  and  (!3utii'orIis. 


ENCEINTES. 

173... The  most  simple  mode  of  fortifying  a  position  in  a 
permanent  manner,  consists  in  enclosing  it  with  a  rampart, 
surmounted  by  a  parapet  with  a  ditch,  the  scarj)  of  which, 
when  dry,  is  revetted  with  masonry,  and  so  covered  by  an 
earthen  luask  that  it  cannot  be  breached  exce])t  by  batteries 
placed  on  the  border  of  the  counterscarp. 

174. ..An  enclosed  line  of  fortification  of  tliis  simple 
character  is  termed  the  enceinte,  the  bodj/  of  the  place,  or  the 
main  enclomirc. 

175... The  general  outline  of  the  enceinte  may  be  curvi- 
linear, or  a  polygonal  figure  of  any  cluiracter. 

176... System  of  Foiitification.  Although  an  infinite 
diversity  of  figures  may  thus  be  presented  in  the  outline 
or  plan  of  the  enceinte,  they  may  be  all  classed  under  four 
heads,  to  each  of  which  engineers  generally  have  applied 


74      ELEMENTS  OF  THE  PLAN  OF  ENCEINTES  AND  OUTWORKS. 

the  term,  si/stem  of  fortification.  These  four  classes  are  :  1, 
the  circular  or  curvilinear  si/stcm;  2,  the  pob/r/onal  qy  capon- 
Jiitre  s)/stcm ;   3,  the  tcnailled  system ;  4,  the  bastioned  system. 

177. ..The  term  method  of  fortification,  instead  of  system, 
is  now  usually  a})plicd  to  the  manner  of  fortifying,  which 
is  generally  prevalent  in  any  country;  or  to  the  mode 
adopted  by  any  individual,  as  the  German  method,  Vau- 
ban's  method,  etc. 

178.... Circular  System.  The  circular  system  consists 
of  an  enceinte,  the  plan  of  which  is  circular,  or  curvilinear. 

179... Polygonal  System.  In  the  polygonal  system,  tlie 
plan  is  either  a  polygon,  with  salient  angles  alone,  PI.  8, 
Fig.  72,  each  side  of  which,  A  A,  is  flanked  by  a  casemated 
caponniere,  C,  placed  in  the  ditch,  D,  and  midway  between 
the  two  salients,  A ;  or  else  each  side  of  the  polygon  is 
broken  inward  at  the  centre,  so  as  to  form  a  slight  re-en- 
tering, PI.  8,  Figs.  73,  74,  75,  76,  77,  to  procure  a  casemated 
flanking  arrangement,  F F,  for  the  caponnieres,  C,  which 
occupy  these  re-enterings,  and  also,  in  some  cases,  to  flank 
works  in  advance  of  the  enceinte. 

180...Tenailled  System.  The  tcnailled  system,  PI.  8, 
Fig.  78,  consists  of  a  tcnailled  line,  the  re-entering  angles 
of  which  are  between  90°  and  100°,  and  the  salient  angles 
not  less  than  G0°. 

181...Bastioned  System.  The  bastioned  system,  Fig.  79, 
consists  of  lunettes  or  bastions  connected  by  curtains,  DD, 
between  the  extremities  of  their  flanks,  B  D.  The  bastions 
usually  consist  of  two  faces  and  two  flanks,  the  scarps  of 
each  of  which  are  plane  surfaces.  In  most  of  the  older 
fortifications,  and  in  a  few  of  the  more  recent  works  in 
Europe,  the  flank  is  broken  ;  the  portion  of  it  at  the  shoul- 
der angle  forming  a  projecting  mass,  which  is  termed  an 
orillon,  whilst  the  portion  between  the  orillon  and  the 
enceinte  curtain  is  retired,  or  brought  in  toward  the  inte- 
rior of  the  bastion,  and  is  thus  partially  covered  by  the 
orillon  from  Are,  except  in  the  prolongation  of  the  enceinte 
ditch.  In  some  cases  the  plan  of  the  orillon,  as  well  as 
that  of  the  retired  flank,  is  curvilinear;  in  others  they  are 
both  rectilinear. 


OUTWORKS    AND    DETACHED    WORKS.  75 

182. ..Front  of  Fortification.  The  term  frotit  of  fortifi- 
cat/on  is  applied  cither  to  tlie  portion  of  tlie  enceinte  com- 
prised between  tlic  capitals  of  two  adjacent  salient  angles  of 
the  polygon,  or  to  tliis  portion  and  any  other  works  within 
or  beyond  it  which  are  comprised  between  two  adjacent 
capitals,  and  arc  connected  with  this  portion  by  relations  of 
defence. 


©utiuorlij)  aiul  gctarhed  Morli.s, 


183... A  work  consisting  of  an  enceinte  alone  is  more  or 
less  exposed  to  surprise,  as  it  must  have  outlets  of  some 
description  to  keep  up  a  communication  with  the  exterior 
and  a  bridge,  or  other  means  for  crossing  the  ditch.  But 
this  is  not  the  only  defect  of  a  fortification  of  this  simple 
character;  for,  having  no  covers  beyond  the  ditch  for  its 
garrison,  their  action  must  be  restricted  to  what  may  be 
termed  a  passive  resistance  alone;  as,  in  any  attempt  to 
operate  on  the  exterior,  they  are  exposed  to  fire  so  soon  as 
they  emerge  from  the  ditch  ;  and  in  a  retreat  toward  the 
work,  if  closely  pursued  l)y  the  assailant,  they  will  not  only 
run  the  risk  of  being  cut  oft",  but  a  retreat  under  such  cir- 
cumstances may  lead  to  the  capture  of  the  work  itself,  by 
the  assailant  being  enabled  to  enter  with  the  retreating 
force. 

184... To  [irovide  against  dangers  of  so  grave  a  character, 
engineers  have  devised  other  defences  beyond  the  ditch, 
and  which  the}'  have  placed  in  immediate  defensive  rela- 
tions with  the  enceinte,  being  under  its  fire  and  in  positions 
where,  if  assaulted,  they  can  1)C  readily  succored  by  the  gar- 
rison. To  Uiis  class  of  exterior  defences  the  term  outworks 
has  been  applied.  The  works  which  come  under  tliis  head 
are  the  covered-way^  the  ienaiUc^  the  demUunc^  the  oounfcr- 
f/nard,  the  rcdouhf  or  rcditif,  tlie  tcnadlou,  the  kornwork  and 
the  crown-work. 


76  OUTWORKS  AND  DETACHED  WORKS. 

185...CovERED-AVAY.  The  covered-way,  as  its  name  im- 
ports, is  an  open  corridor  or  passage,  masked  from  tlie 
assailant's  view  by  an  embankment,  whicli  borders  the 
ditch  of  the  enceinte  alone  when  there  are  no  other  out- 
Avorks ;  but,  in  the  contrary-  case,  also  envelops  the  ditches 
of  these,  forming  thus  a  continuous  covered  line  of  commu- 
nication around  the  fortilication. 

186. ..The  covering  embankment  itself  is  arranged  tow^ard 
the  covered-way  like  an  ordinar}^  parapet,  and  it  receives  on 
the  exterior  a  gentle  slope  or  glacis.  By  this  arrangement 
the  garrison  have  a  covered  j)osition  beyond  the  ditch 
where  thej^  can  assemble  with  safety,  either  for  the  purpose 
of  making  a  sortie  or  to  guard  the  ditches  and  the  commu- 
nications across  them;  and  which  affords  them  also  a  secure 
point  of  retreat  if  repulsed  in  a  sortie,  as  a  reserve  left 
in  the  covered-way  will  be  at  hand  to  check  the  pursuit 
hy  their  fire,  and  enable  the  retreating  party  to  gain  the 
enceinte. 

187... Places  of  Arms.  The  covered-way,  from  the  direc- 
tion given  to  the  counterscarps  of  the  enceinte  and  out- 
works, forms  a  line  of  communication  with  salient  and 
re-entering  parts,  Pis.  8,  9,  Figs.  80  to  85.  The  salient  por- 
tions, S,  are  termed  salient  'places  of  arms ;  and  the  re-enter- 
ing parts  the  re-entering  places  of  arms. 

188... The  salient  places  of  arms,  it  will  be  seen,  result 
from  the  general  plan  of  the  covered-way;  but  the  re-enter- 
ing places  of  arms  are  formed  b}'  changing  the  directions 
of  the  two  branches  where  they  form  the  re-enterings,  i?,  so 
as  to  make  a  salient  Avithin  the  re-entcrings;  thus  enlarging 
the  covered-w^ay  at  these  points,  and  procuring  a  flanking 
arrangement,  by  which  the  glacis  can  be  swept,  and  a  cross- 
fire be  brought  to  bear  on  the  ground  in  advance  of  the 
salients. 

189... Traverses.  The  covered-way,  from  its  position  and 
the  usually  slight  command  given  to  the  crest  of  its  glacis, 
is  very  much  exposed  to  the  efltects  of  an  enfilading  fire. 
With  a  view  to  remedy  this  defect,  and  also  to  enable  the 
garrison  to  dispute,  foot  by  foot,  the  possession  of  this  out- 


OUTWORKS  AND  DETACHED  WORKS.  77 

work  by  the  assailant,  earthen  masks,  formed  like  an  ordi- 
nary parapet,  and  termed  traverses,  are  thrown  np  across  it. 
The  traverses  usually  extend  to  the  counterscarp,  the  wall 
of  which  is  built  up  to  sustain  them.  At  the  end  toward 
the  glacis  a  passage,  or  deiile,  is  left  between  them  and  the 
covering  embankment,  to  admit  of  a  free  communication 
throughout  the  covered-wa}'. 

100...Tenaille.  The  teiuxille  is  a  low  work,  placed  in  the 
re-entering  formed  in  the  enceinte  ditch  by  the  curtain  and 
flanks  of  the  bastioned  system,  being  isolated  by  a  ditch 
between  it  and  these  parts  of  the  enceinte.  Its  chief  pur- 
pose is  to  serve  as  a  mask,  covering  the  scarp  walls  of  this 
re-entering  from  tire  as  well  as  the  outlets  to  the  enceinte 
ditch,  which  are  usually  placed  in  the  centre  of  the  curtains. 

101... The  tenaille  has  received  various  forms  from  engi- 
neers. In  some  cases  it  has  been  made  with  two  faces  or 
wings,  nuiking  a  re-entering  angle  opposite  the  centre  of  the 
enceinte  curtain.  In  others  the  two  wings,  instead  of  being 
prolonged  until  the}-  meet,  are  connected  by  a  short  curtain 
parallel  to  that  of  the  enceinte.  In  some  examples,  it  has 
the  form  of  a  small  bastioned  front.  In  others,  it  consists 
of  two  flanks  connected  by  a  curtain.  The  flanks  in  some 
cases  have  been  casemated  for  guns  and  mortars.  The  te- 
naille is  usually  revetted  with  nuisonry,  l)otli  in  front  and 
rear.  In  some  cases  the  ends  alone,  toward  the  flanks  of 
the  enceinte,  are  revetted,  the  intermediate  portions  consist- 
ing of  an  ordinary  earthen  parapet,  without  either  scarp  or 
gorge  wall. 

192. ..Demilune.  The  demilune,  PI.  9,  Figs.  81,  82,  83, 
84,  is  a  work  in  the  form  of  a  redan,  D,  placed  in  front  of 
the  enceinte  curtain,  which  it  masks  from  fire,  as  well  as  a 
portion  of  each  face  of  the  enceinte,  at  the  shoulder  angles 
of  the  bastions.  It  is  isolated  from  the  enceinte  by  the 
nuiin  ditch,  and  from  its  own  covered-way  by  its  ditch. 
From  its  importance  the  scarp  and  gorge  of  the  demilune 
are  generally  revetted,  though  in  some  cases  the  revetemeut 
has  been  omitted. 

193...CouNTER(JUArj).     The  countcrg^iard  is  an   isolated 


78  OUTWORKS  AND  DETACHED  WORKS. 

work,  C,  Fig.  83,  in  the  form  of  a  redan,  which  envelops 
the  faces  of  a  bastion.  In  some  cases  it  consists  simply  of 
an  earthen  mask  having  the  profile  of  an  ordinary  parapet; 
but  it  is  usually  revetted  both  in  front  and  rear. 

194. ..Redoubts.  The  term  redoubt,  or  red uit,  is  applied 
to  outworks  placed  within  other  outworks;  their  object 
being  to  strengthen  the  defence  of  the  principal  work. 

195... A  work  of  this  class  is  usuall}'  placed  within  the 
demilune,  and  is  termed  the  demilune  redoubt.  Small  works 
of  this  kind  are  also  placed  in  the  salient  and  re-entering 
places  of  arms  of  the  covered- way,  and  are  termed  the 
redoubt  of  the  salient,  or  re-entering  place  of  arms.  These 
redoubts  are,  in  some  cases,  simple  earthen  works ;  in 
others,  they  are  revetted ;  and  in  others,  casemated,  both 
for  the  service  of  artillery  and  small  arms. 

196...TENAILLON.  The  term  tenaillon,  PI.  9,  Fig.  81,  is 
applied  to  a  kind  of  face  cover,  or  counterguard,  7\  of  the 
demilune.  It  is  only  to  be  met  with  in  some  of  the  old 
fortified  places  of  Europe,  and  was  added  to  give  more 
strength  to  the  fronts  where  the  demilune  was  too  small. 

197...IIORNWORK.  The  horn  work,  PI.  9,  Fig.  82,  usually 
consists  of  a  bastioned  front,  H,  with  the  ordinary  outworks, 
having  two  long  branches,  li^F,  or  wings,  which  rest  upon 
two  adjacent  bastions,  or  two  adjacent  demilunes,  D D,  of 
the  enceinte — its  covered-way  forming,  with  that  of  the 
enceinte,  a  continuous  line  of  communication.  The  object 
of  this  outwork  is  to  strengthen  a  salient  or  other  weak 
portion  of  the  enceinte. 

198...CiiowN-woRK.  The  crown-work,  PI.  9,  Fig.  83, 
consists  of  two  or  more  bastioned  fronts,  C,  with  their  out- 
works, })laced  in  front  of  some  portion  of  the  enceinte, 
to  give  it  additional  strength.  It  is  terminated,  like  the 
hornwork,  by  two  wings,  J^F,  which  rest  either  upon  the 
enceinte,  or  upon  the  demilunes,  D  D.  Its  covered-way, 
like  that  of  the  hornwork,  forms  a  continuous  communica- 
tion with  that  of  the  enceinte. 

199... Detached  Works.  There  are  two  other  classes  of 
exterior   defences   besides    the    outworks,  termed   detached 


INTERIOR    RETRENCHMENTS.  79 

xmrks  and  advanced  woi-Jis,  the  object  of  which  is  either  to 
strengthen  some  M^eak  portion  of  the  enceinte  or  to  occupy 
positions  which  would  he  of  advantage  to  an  assailant  in 
his  attacks  on  the  enceinte. 

200... Detached  works  are  such  as  are  placed  beyond  the 
covered-way  of  the  enceinte,  but  within  the  range  and 
support  of  its  fire.  Advanced  works  are  such  as,  from  their 
advanced  position,  receiving  but  little  or  no  support  from 
the  fire  of  the  enceinte,  must  rely  upon  their  own  resources 
for  defence.  The  former  class  are  usually  open  in  the  rear, 
so  that  their  interior  may  be  exposed  to  the  fire  of  the 
enceinte;  Avhilst  the  latter  should  be  closed  throughout  and 
of  sufficient  strength  of  profile  to  secure  them  from  an  open 
assault. 

201... In  ri.  9,  Fig.  84,  is  a  detached  work,  L,  flanked  by 
the  demilunes,  D,  of  the  enceinte.  The  plan  of  this  work 
is  a  lunette,  with  its  covered-way  and  places  of  arms,  R 
and  S. 


interior  llclrcnchmtnt.^. 


202. ..Besides  the  works  exterior  to  the  enceinte,  the 
object  of  which  is  to  retard  the  assailant  ui  his  attempts  to 
enter  it  by  breaching,  engineers  have  placed  within  it  other 
works  which,  in  some  cases,  are  designed  simply  to  enable 
the  garrison  to  make  an  eft'ectual  defence  of  the  breach, 
when  the  assault  upon  it  is  made,  and  give  them  a  secure 
point  of  retreat  and  safety  when  driven  from  it;  and  in 
others,  these  interior  works  are  chiefly  designed  to  bring  a 
plunging  fire  to  bear  on  the  assailant's  siege  Avorks  exterior 
to  the  enceinte.  The  former  class,  intended  for  the  defence 
of  the  breach  alone,  are  termed  interior  retrenchments ;  and 
the  latter,  cavaliers. 

203. ..Interior  retrenchments  are  either  placed  within  the 


80  INTERIOR   RETRENCHMENTS. 

bastions,  which  are  the  parts  of  the  enceinte  usually  breach- 
ed, or  in  rear  of  their  gorges.  Those  which  are  placed 
within  the  bastions  extend  across  them,  either  between  the 
fiices  or  between  the  Hanks.  When  placed  at  the  gorge, 
they  connect  the  two  adjacent  curtains. 

204. ..The  plan  of  these  works  varies  with  their  position, 
the  size  of  the  bastions,  or  the  more  or  less  of  openness  of 
their  salient  angles. 

205. ..In  small  bastions  with  acute  salients,  when  the 
retrenchment  rests  upon  the  faces,  it  usually  receives  the 
form  of  a  tenaille  or  inverted  redan,  the  angle  of  the 
tenaille  being  about  100°.  When  the  bastions  are  large 
and  the  salient  angle  quite  open  or  obtuse,  the  retrench- 
ment may  receive  the  form  of  a  small  bastioned  front,  PI. 
9,  Fig.  85,  resting  upon  the  faces. 

206. ..Either  of  these  forms  may,  in  like  manner,  be  used, 
when  the  retrenclinient  rests  upon  the  flanks  of  the  bastion. 
But  as  this  position  enables  a  retrenchment  of  the  form  of 
an  ordinary  redan  to  have  its  ditches  swept  by  the  fire  of 
the  flanks  of  the  adjacent  bastions,  this  form  is  in  some 
cases  used  in  preference. 

207... When  placed  between  two  curtains  at  the  gorge  of 
a  bastion,  the  plan  of  the  entrenchment  is  always  a  bas- 
tioned front. 

208... Cavaliers  are  placed  either  upon  the  curtains  or 
within  the  bastions.  The  latter  is  the  more  usual  position 
selected  for  them.  Their  plan  in  this  position  is  usually 
that  of  a  lunette,  the  faces  and  flanks  of  which  are  parallel 
to  those  of  the  enveloping  bastion.  Cavaliers  receive  a 
considerable  command  over  the  parapet  of  the  enceinte, 
and,  in  some  cases,  they  are  arranged  with  a  tier  of  case- 
mated  fire,  above  which  is  an  open  battery. 

209... Interior  retrenchments  arc  usually  constructed  with 
a  revetted  scarp  and  counterscarp,  to  secure  them  from  an 
open  assault;  and,  in  some  cases,  a  covered-way,  with  a 
small  re-entering  place  of  arms,  li,  PI.  9,  Fig.  85,  closed  by 
traverses,  is  arranged  in  advance  of  the  ditch,  to  insure  the 
safe  retreat  of  the  si-arrison  when  driven  from  the  breach. 


BASTIONED    SYSTEM.  81 


lafjtioned  ^nj)t([ni 


210. ..A  bastioned  enceinte  consists  of  a  series  of  bas- 
tions which  occupy  the  salient  angles  of  the  pol^-gon, 
within  which  the  enceinte  is  enclosed;  the  flanks  of  the 
bastions  being  usually  connected  by  straight  curtains. 

211... The  sides  of  the  polygon  which  connect  the  salient 
angles  of  the  bastions,  are  termed  the  exterior  sides,  in  con- 
tradistinction to  the  sides  of  an  interior  polygon,  which, 
being  parallel  to  the  first  and  occupying  the  positions  of 
the  curtains,  are  termed  the  interior  sides. 

212... The  bastioned  enceinte,  when  its  relief  and  plan 
are  suitably  arranged,  possesses  the  advantage  of  having  its 
ditches  thoroughly  swept  from  within  the  enceinte  itself, 
thus  securing  the  flanking  arrangement  of  the  scarp,  whilst 
the  garrison  also  is  kept  within  the  enceinte  under  the 
immediate  eye  and  orders  of  their  commander,  up  to  the 
moment  of  the  fall  of  the  work;  of  bringing  a  cross  and 
flank  fire  to  bear  upon  the  approaches  on  the  salients  of 
the  enceinte  in  the  directions  of  the  capitals  of  the  bas- 
tions; and  furnishing  a  strong  direct  and  cross  fire  upon 
the  site  in  advance  of  the  curtains  and  the  faces  of  the 
bastions. 

213... The  principal  objections  urged  against  the  bas- 
tioned system  are,  that  its  chief  characteristic  —  a  perfect 
flanking  disposition  for  the  entire  line  of  the  scarp  —  is 
attainable  only  under  certain  relations  between  the  re- 
quisite relief  for  a  permanent  work  and  the  length  of  the 
exterior  side  and  curtain,  which,  therefore,  restricts  it  in  its 
application  to  fortification  of  a  permanent  character;  that, 
in  order  to  secure  sufficient  length  of  flank  for  an  eflective 
flanking  disposition,  the  angle  between  the  face  of  the 
bastion  and  the  exterior  side,  termed  the  diminished  angle  of 
the  polygon,  has  to  be  made  so  great  as  to  decrease  consid- 
6 


82  BASTIONED    SYSTEM. 

erably  the  space  enclosed  within  the  polygon,  whilst  the 
development  of  the  line.of  the  enceinte  is  greatly  increased 
by  it;  that  this  direction,  necessarily  given  to  the  faces 
from  this  cause,  throws  their  prolongations  in  positions 
very  favorable  to  the  erection  of  entilading  batteries  against 
them;  that  the  flanks,  upon  which  the  whole  system  is 
based,  lie  in  positions  in  which,  like  the  faces,  they  can  be 
not  only  easily  eniiladed,  but  are  farther  exposed  to  a 
reverse  fire  from  shot  which  may  pass  over  the  parapet  of 
the  faces  as  well  as  the  opposite  flank  ;  and  that  these 
objections  are  the  stronger  as  the  salient  angles  of  the 
polygon  are  smaller,  or  as  the  number  of  sides  is  de- 
creased. 

214... Besides  these  objections,  which,  to  a  certain  extent, 
are  well  founded,  where  the  defensive  arrangements  are 
chiefly  open,  as  is  the  case  in  most  land  fronts,  others  have 
been  urged  against  this  system,  which,  being  rather  of  a 
comparative  character,  as  showing  the  advantages  of  other 
systems  over  this,  will  best  be  examined  elsewhere. 

215... As  the  plan  and  relief  of  the  bastioned  enceinte, 
employed  among  engineers  of  the  present  day,  differ  in  no 
very  material  points  from  those  adopted  about  the  period 
of  Vauban,  when  the  art  of  fortification  assumed  somewhat 
less  of  mere  mechanical  routine,  it  has  become  the  j^ractice 
in  military  schools  in  Europe  to  deduce,  from  the  descrip- 
tion of  the  bastioned  method  of  Vauban  and  his  immediate 
successors,  the  principles  upon  which  the  forms  and  dimen- 
sions, both  of  the  enceinte  and  its  outworks,  as  well  as  their 
defensive  relations,  are  based.  As  this  course  has  the  fur- 
ther advantage  of  exhibiting  the  views  of  men  who  are 
still  looked  to  as  the  safest  authorities  in  the  art,  whilst 
it  gives,  at  the  same  time,  a  history  of  its  progress  and 
changes  from  the  period  when  it  may  be  said  to  have  first 
broken  loose  from  the  trammels  of  mere  routine  up  to  the 
present  day,  it  has  been  also  adopted  as  the  basis  of 
the  instruction  given  on  this   subject  in   this   institution. 


vauban's  first  method.  83 


taubnufj  (^irfit'Pethol 


216...Vanl)an  has  left  examples  of  three  different  meth- 
ods in  the  places  planned  by  him.  The  Fortress  of  New 
Brisac  is  fortilied  after  liis  third  method;  those  of  Landau 
and  Befort  after  his  second ;  but  the  greater  part  of  the 
places  fortified  by  him  are  planned  according  to  his  first,  or 
earliest  method. 

217. ..Note.  In  the  following  description  of  the  methods 
of  Vauban,  Cormontaingne  and  some  other  French  authors, 
the  English  yard  has  been  substituted  for  the  French  half 
toisc  and  the  7netrc,  each  of  which  is  so  nearly  the  equivalent 
of  the  yard  as  not  to  affect  in  any  sensible  manner  the  prin- 
ciples or  the  defensive  relations  of  the  parts.  In  like  man- 
ner the  English  foot  has  been  substituted  for  the  French 
foot. 

218. ..Profile  of. Enceinte.  In  the  ju-ofile  of  this  method, 
Fig.  1,  n.  1,  the  scarp  wall  is  36  feet  high,  its  slope  being 
five  perpendicular  to  one  of  base ;  surmounting  .this  is 
another  wall  from  4  to  G  feet  high,  the  object  of  which  is  to 
sustain  the  exterior  of  the  ])arapet.  The  parapet  is  18  feet 
thick,  the  su})erior  slope  being  I ;  the  interior  crest  is  8  feet 
above  the  terrcplein,  which  is  42  feet  in  width.  The  mean 
command  of  the  interior  crest  above  the  site  is  about  26  feet. 
The  bottom  of  the  ditch  is  about  17|  feet  below  the  site. 

219... Plan  of  Enceinte.  Vauban  adopted  no  arbitrary 
or  invariable  combination  of  parts  in  his  methods.  His 
great  excellence  as  an  engineer  is  shown  in  the  acknowl- 
edged skill  with  which  he  adapted  the  fortifications  he 
planned  to  the  defensive  requirements  of  the  sites.  Select- 
ing long,  medium,  or  short  exterior  sides,  and  varying  the 
lengths  and  directions  of  the  faces  and  flanks  so  as  to  pro- 
cure the  best  command  over  the  exterior  ground,  and  to 
withdraw  these  parts  from  the  enfilading  views  of  the  assail- 


84  vauban's  first  method. 

aiit.  Ill  his  works,  however,  lie  has  generality  taken  360 
yards  as  the  greatest  limit  of  the  exterior  side ;  the  perpen- 
dicular of  the  front  ^  when  the  polygon  is  a  square;  |  for 
the  pentagon;  and  I  for  all  liigher  polygons.^  With  these 
starting  points  he  procured  diminished  angles  which  gave 
more  than  60°  to  the  salient  angles  of  the  bastions  in  all 
cases,  and  flanks  of  suitable  length  both  to  flank  the  main 
ditch  and  to  encounter  with  advantage  the  counter-batteries 
which  could  be  erected  against  them.  The  following  con- 
structions, both  for  the  enceinte  and  outworks,  are  taken 
from  the  best  French  authorities  as  adopted  by  him  for 
polygons  higher  than  the  pentagon. 

220... In  the  plan  or  trape,  Fig.  2,  PI.  1,  the  magistral  is 
taken  as  the  directing  line;  the  exterior  side  is  360  yards; 
on  the  perpendicular  of  the  front  a  distance  of  I  the  exterior 
side  is  set  off;  lines  drawn  through  this  point  and  the  ex- 
tremities of  the  exterior  side,  determine  the  directions  of 
the  faces  and  the  lines  of  defence;  from  the  salients  a  dis- 
tance equal  to  ^  of  the  exterior  side  is  set  off,  which  gives 
the  lengths  of  the  faces  and  the  positions  of  the  shoulder 
angles ;  the  flank  is  drawn  by  taking  the  opposite  shoulder 
angle  as  a  centre ;  and  with  a  radius  equal  to  the  distance 
between  the  shoulder  angles,  describing  an  arc  to  intersect 
the  line  of  defence,  the  chord  of  this  arc  is  the  flank;  the 
curtain  is  drawn  by  joining  the  extremities  of  the  flanks. 
By  this  construction  the  flanks  Avill  be  about  54  yards ;  the 
curtain,  146 ;  and  the  lines  of  defence,  267 — the  length  of 
these  being  determined  so  that  the  salients  of  the  bastions 
can  be  defended  with  the  rampart  gun,  or  ivall-jnece. 

221 . .  .Tenaille.  In  many  of  the  places  constructed  before 
Vauban's  time  there  was  a  low  work,  enveloping  the  en- 
ceinte and  connected  with  it,  called  a  fausse-braie.  This 
work,  which  had  many  defects,  was  suppressed  by  Vauban, 
who  was  the  first  to  use  the  tenaille  in  its  place.  The  tenaille 
has  many  valuable  properties :  it  covers  the  arched  commu- 
nication, or  postern,  under  the  curtain  ;  masks  the  masonry 
of  the  curtain  and  flanks,  so  that  a  breach  cannot  be  made 
in   them,  and  in  this  way  prevents  retrenchments,  resting 


vauban's  first  method.  85 

against  those  parts,  from  being  turned;  a  place  of  arms  is 
formed  between  it  and  the  curtain,  wliere  troops  can  be  as- 
sembled for  sorties  in  the  ditches ;  finall}^  its  fire  sweeps 
the  ditch  and  counterscarp,  and  helps  to  cover  the  retreat 
of  troops  from  the  other  outworks.  The  tenaille  is  sepa- 
rated from  the  curtain  by  a  ditch  10  yards  wide,  and  from 
the  flanks  by  ditches  of  6  yards.  The  form  of  the  tenaille, 
as  used  by  Yauban,  was  variable  :  in  some  cases  he  made  it 
with  a  curtain  and  two  small  flanks  parallel  to  those  of  the 
enceinte;  in  others,  it  consisted  simply  of  two  wings  placed 
on  the  prolongations  of  the  faces;  and,  finally,  he  gave  it 
the  form  in  Fig,  2,  with  a  small  curtain  and  two  wings, 
which  is  the  one  at  present  most  generally  adopted.  The 
relief  of  the  tenaille  is  so  arranged  as  not  to  mask  the  fire 
of  the  flanks  on  the  ditch  of  the  enceinte  along  the  faces ; 
for  this  purpose  Vauban  places  its  interior  crest  on  a  level 
with  the  site,  or  a  little  below  it. 

222. ..Main  Ditch.  Yauban  followed  no  invariable  rule 
in  regulating  the  dimensions  of  the  enceinte  ditch  ;  its 
most  usual  width  at  the  salients  of  the  bastions,  where  the 
counterscarp  is  an  arc  of  a  circle,  is  about  36  yards;  the 
rest  of  the  counterscarp  is  tangent  to  this  arc,  and  directed 
upon  the  opposite  shoulder  angles.  ^ 

223... Demilune  and  Reuuit.  Yauban  increased  the  di- 
mensions of  the  demilune  which  had  been  used  previous  to 
his  time.  The  object  of  this  work  is  to  secure  the  gates  of 
the  place  from  a  surprise;  to  mask  from  the  enemy's  batte- 
ries the  flanks  and  curtain  of  the  enceinte;  and  give  cross 
fires  on  the  salients  of  the  bastions.  The  plan  and  dimen- 
sions of  the  demilune  vary  also  in  Yanban's  works.  Its 
magistral  is  generally  laid  out  by  taking  a  point  on  the 
bastion  face  at  10  yards  from  the  shoulder  angle,  and  draw- 
ing a  line  from  this  point  to  the  perpendicular  of  the  front, 
so  as  to  make  the  face  of  the  demilune  equal  to  f  of  the 
exterior  side.  The  parapet  of  the  demilune  is  the  same  as 
that  of  the  enceinte;  its  command  is  3  feet  less  than  that 
of  the  enceinte.  Alt  the  outworks  in  this  system  are  com- 
manded by  the  enceinte ;  the  outworks  most  advanced 
being  also  commanded  by  those  in  rear. 


86  VAUBAX'S    FIRST    METHOD. 

224. ..To  strengthen  the  demilune,  and  secure  for  the 
troops  entrusted  with  its  defence  a  safe  retreat  when  it  is 
carried,  Yauban  placed  in  it  a  small  redoubt.  This  work, 
in  some  instances,  was  only  a  simple  crenated  wall,  with  a 
ditch  in  front;  sometimes  it  was  made  of  earth,  and  after 
the  commencement  of  the  siege. 

225... The  ditch  of  the  demilune  is  generally  about  24 
yards  wide,  and  of  the  same  depth  as  that  of  the  enceinte; 
its  counterscarp  and  that  of  the  enceinte  forming  a  contin- 
uous wall. 

226...CovEEED-WAY.  The  covered-way  envelops  the  en- 
tire counterscarp.  Vauban  placed  a  high  value  on  this 
work,  which,  to  use  his  own  words,  "  Costs  less  to  the 
defence  and  more  to  the  assailant  than  any  other  w^ork." 
The  covered-way  prevents  all  access  to  the  ditch,  by  a 
♦  strong  fire  of  musketry,  which  sweeps  all  the  exterior 
ground ;  it  is  a  secure  position,  where  troops  can  be  as- 
sembled in  safety  for  sorties ;  it  covers  the  retreat  of  troops 
from  the  exterior  into  the  other  works.  The  general  width 
of  the  covered-way  is  12  yards.  To  set  out  the  re-entering 
place  of  arms,  two  points  are  taken  at  20  yards  from  the 
re-entering  angle,  made  by  the  interior  crests  of  the  covered- 
ways  of  the  demilune  and  bastion,  and  upon  these  crests, 
and  from  these  points  as  centres,  with  radii  of  24  yards, 
arcs  are  described;  the  point  of  their  intersections  being 
joined  with  their  centres,  gives  the  crests  of  the  re-entering 
place  of  arms.  The  parapet  of  the  covered-wa}^  is  termi- 
nated in  a  glacis,  the  foot  of  which  is  from  40  to  50  yards 
from  the  interior  crest. 

227. ..Traverses.  To  close  the  place  of  arms,  and  enable 
the  troops  to  defend  the  covered-way  foot  by  foot,  traverses 
of  earth  formed  into  parapets  are  placed  at  the  places  of 
arms.  Defiles  or  passages  of  4  feet  are  left  between  the  trav- 
erses and  the  crest  of  the  covered-way,  for  the  circulation 
of  the  troops. 

The  covered-way  is  palisaded  to  prevent  surprise. 

228 . . . Communications.  The  conimunicaiions  constitute  an 
important  part  of  every  system.     In  Vauban's  front,  ramps 


vauban's  first  method.  87 

are  made  to  ascend  from  the  plane  of  sight  to  the  terre- 
plein.  A  postern  is  made  under  the  curtain,  to  communi- 
cate from  the  interior  with  the  ditch;  another  postern  is 
made  under  the  tenaille,  to  lead  to  the  demilune;  a  double 
caponnih'c^  which  is  a  passage  covered  on  each  side  by  a 
parapet  terminated  in  a  glacis  toward  the  ditch,  covers  the 
communication  through  the  ditch  to  the  gorge  of  the  demi- 
lune; single  caponnieres  are  placed  in  the  ditch  of  the 
demilune,  and  cover  the  troops  from  the  enemy's  fire 
through  its  ditch;  stairs  are  placed  at  the  gorges  of  the 
tenaille  and  demilune,  and  along  the  counterscarp  at  the 
places  of  arms,  to  ascend  from  the  ditch  to  the  terre[)leins 
of  those  works.  To  communicate  with  the  exterior,  nar- 
row openings  are  made  in  the  faces  of  the  re-entering  place 
of  arms,  to  lead  from  the  terrepleins  to  the  glacis;  they 
are  termed  sortie  passages,  or  sally-ports,  and  are  closed  b}- 
barriers. 

REMARKS. 

229. ..Enceinte.  In  the  trage  adopted  by  Vauban  for 
the  enceinte,  it  may  be  observed  that  the  length  and  posi- 
tions of  the  lines  of  the  front  resulting  from  it  are  in  good 
defensive  relations,  both  for  cannon  and  small  arms. 

230... In  the  first  place,  the  foot  of  the  scarp,  throughout 
the  length  of  the  curtain  and  tlie  bastions,  is  thoroughly 
exposed  to  the  fire  of  the  flanks,  whicli,  from  the  dimin- 
ished angle  assumed  in  the  hexigon  and  higher  polygons, 
which  is  about  18|°,  and  the  curtain  angle,  which  is  nearly 
100° — can  sweep  both  the  curtain  scarp  and  that  of  the 
bastion  face  from  an  embrasure  placed  at  the  curtain 
angle. 

231... In  the  second  place,  the  length  of  the  flank  is  suf- 
ficient to  contain  as  many  cannon,  at  least,  as  the  assailant 
can  place  to  counter-batter  the  flank  fVoni  the  glacis  crest 
opposite  the  flank;  and  the  flank  can  also  bring  an  efficient 
fire  of  small  arms  to  bear  on  this  battery  of  the  assailant. 

232. ..The  bastions  are  of  good  size,  and  would  admit  of 


88  vauban's  first  method. 

efficient  interior  retrenchments  being  thrown  np  in  them, 
although  Yauban  does  not  indicate  this  auxiliary  means  in 
his  1.*^  Method. 

233...TENAILLE.  Yauban  substituted  the  tenaille  for  the 
fausse-braie,  as  this  latter  work  facilitated  an  escalade,  and, 
moreover,  exposed  the  troops  in  it  to  the  annoyance  of  the 
splinters  from  the  walls  behind,  when  exposed  to  the  as- 
sailant's fire.  The  tenaille  was  devised  mainlj-  to  masl^the 
scarp  wall  of  the  curtain  and  flanks,  whilst  its  relief  was  so 
regulated  as  not  to  intercept  the  tire  of  the  flanks  on  the 
enceinte  ditch  before  the  bastion  faces.  The  plan  of  the 
earlier  tenailles  consisted  of  two  flanks  connected  by  a  cur- 
tain, which  were  parallel  to  the  same  lines  of  the  enceinte. 
This  form  was  subsequently  abandoned,  as  the  flanks  were 
found  to  be  exposed  to  both  an  enfilading  and  reverse  fire 
from  the  assailant's  positions  in  front  of  the  enceinte;  and 
the  one  now  in  most  general  nse,  consisting  either  of  two 
wings  simply,  or  of  two  wings  connected  by  a  short  curtain, 
adopted  in  its  place. 

The  tenaille,  however,  only  partially  subserves  its  object, 
as  it  does  not  cover  the  entire  height  of  the  scarp  of  the 
enceinte  curtain  and  flanks;  and,  what  is  a  more  serious 
defect,  it  leaves  the  entire  height  of  scarp  of  that  portion 
of  the  curtain  opposite  to  thc^ditch,  between  the  tenaille 
and  the  bastion  flank,  entirely  exposed  from  the  same  posi- 
tion, and  liable  to  be  breached. 

234... Demilune.  From  the  small  size  of  this  work,  it 
gives  but  little  cover  to  any  portion  of  the  enceinte  except 
the  curtain.  It  is  not  sufficiently  thrown  to  the  front  to 
give  a  good  volume  of  cross  fire  on  the  glacis  in  advance 
of  the  bastion  salients  ;  and  the  re-entering  formed  at  this 
point,  by  the  two  adjacent  demilunes,  is,  from  the  same 
cause,  shallow,  and  of  but  little  strength.  Owing  to  this 
last  defect,  the  assailant  Qan  easily  breach  and  storm  the 
enceinte  at  the  same  time  as  the  demilune. 

Besides  these  defects,  the  demilune  is  not  provided  with 
a  permanent  reduit — a  work  necessary  to  enable  the  demi- 
lune to  make  a  vigorous  defence,  by  the  support  it  afi:brds 
the  assailed. 


vauban's  first  method.  89 

235... Covered-way.  From  tlie  width  given  to  the  demi- 
kuie  ditch,  tlie  covered-ways  are  exposed  to  a  slant  reverse 
fire,  from  which  tliey  are  but  l)adly  screened  hy  tlie  trav- 
erses. Their  command  over  the  site  is  rather  too  little. 
Their  main  defect,  however,  is  the  small  size  given  to  the 
re-entering  place  of  arms,  and  the  failure  to  secure  this 
important  position  for  assembling  troops  for  sorties  by  a 
permanent  reduit,  by  which  any  open  attack  of  the  covered- 
way  could  be  prevented. 

280... Ditches.  The  dimensions  given  both  the  enceinte 
and  demilune  ditches  present  a  formidable  obstacle  to  an 
open  assault,  and  render  the  assailant's  passage  of  the  ditch 
by  the  sap  more  difficult.  The  demilune  ditch,  however, 
offers  a  wide  opening,  through  which  the  scarp  of  the  bas- 
tion face  can  be  seen  down  to  its  foot  from  the  assailant's 
batteries  on  the  glacis  crest  in  the  prolongation  of  the  demi- 
lune ditch. 

2o7... Communications.  The  communications  within  the 
enceinte,  and  from  it  to  the  main  ditch,  are  sufficient  and 
convenient  for  the  character  of  the  defence  designed. 
Those  of  tbe  outworks  are  for  the  most  part  narrow,  incon- 
venient, and  badly  screened  from  the  assailant's  fire,  and,, 
therefore,  do  not  furnish  a  good  provision  for  an  active 
defence  beyond  the  enceinte. 

238... Profiles.  The  great  command  over  the  site,  and 
the  high  relief  given  to  the  enceinte,  are  very  much  in 
favor  of  the  defence,  both  as  to  the  eft'ect  of  the  fire  on  the 
assailant's  apprcjaches,  and  for  security  against  an  escalade. 
But,  in  attaining  these  objects,  Vauban  has  left  exposed  to 
the  assailant's  distant  fire  a  considerable  ].)ortion  of  the  scarp 
wall,  which,  being  destroyed,  would  lay  the  enceinte  open 
to  a  surprise. 


90  vauban's  third  method. 


timkiu  i^Itird  pdtoi. 


239... In  his  3d  Method,  PI.  14,  which  differs  from  his 
2d  only  in  some  minor  modifications,  Vauhan  adopted  what 
may  be  termed  a  double  enceinte,  the  interior  one  being 
continuous,  and  consisting  of  small  casemated  bastioned 
towers,  i,  i?,  0,  placed  at  the  angles  of  the  polygon,  which 
are  connected  by  curtains,  P,  Z^  W^  U',  in  the  form  of  bas- 
tioned fronts,  the  flanks  of  which  are  also  casemated,  and 
intended,  with  those  of  the  towers,  to  sweep  the  ditch  of  this 
enceinte. 

240... The  second,  or  exterior  enceinte,  is  not  continuous, 
but  consists  of  large  bastions,  A,  H,  K,  or  counterguards 
with  flanks,  which  cover  the  towers  and  the  faces  of  the 
bastioned  curtain  between  tliem,  and  of  a  tenaille,  which 
lies  between  the  flanks  of  the  counterguards  and  covers 
the  curtain  of  the* interior  enceinte. 

241... In  advance  of  this  exterior  enceinte  is  placed  a 
demilune,  arranged  with  flanks,  which  contains  a  small 
revetted  redoubt,  and  a  covered-way  similar  to  the  one  in 
his  1st  Method. 

242... Plan.  The  lines  joining  the  salients  of  the  coun- 
terguards form  the  exterior  sides,  and  are  taken  at  360 
yards.  The  perpendicular,  CD,  is  one-sixth  of  the  exterior 
side,  or  60  yards.  The  face,  A  H,  one-third  the  exterior 
side,  or  120  yards.  The  flank,  UK,  is  constructed  as  in 
the  1st  Method. 

243. ..The  tenaille  consists  simply  of  two  wings  in  the 
prolongation  of  the  faces  of  the  counterguards  ;  a  ditch  10 
yards  wide  is  left  between  the  tenaille  and  the  flanks  of  the 
counteriJ:uard.  The  o'or£:e  line  of  the  tenaille  and  the 
flanks  of  the  counterguards  lie  on  the  line  LM,  joining  the 
salients  of  the  towers. 

244... To  set  out  the  towers  and  connecting  curtain,  a 


vauban's  third  method.  91 

line,  NT,  is  drawn  parallel  to  L  M,  and  at  16  yards.  The 
flanks,  7?,  Q,  of  tlie  towers  are  drawn  through  points  P,  at 
14  yards  from  N.  The  portion  of  the  flanks,  P,  P,  exterior 
to  the  curtain,  being  12  yards,  and  the  interior  portion, 
P  §,  8  yards.  The  faces  are  found  by  joining  the  points 
L,  P. 

245... The  perpendicular,  T  V,  of  the  bastioned  .?urtain 
is  10  yards.  The  flanks,  Z,  W,  are  on  the  proh)ngations  of 
the  counterguard  flanks.  The  curtain,  WW,  is  parallel  to 
L3L 

246... The  gorge  of  the  counterguard  is  constructed  by 
describing  an  arc  from  L,  as  a  centre,  with  a  radius  of  14 
yards,  and  drawing  a  tangent  to  this  arc  from  the  point 
corresponding  to  Z,  on  the  opposite  flank,  to  Z  W. 

247. ..The  salient,  C",  of  the  demilune  is  at  110  yards  from 
the  point  0,  where  a  line  parallel  to  the  counterguard  face, 
and  30  yards  from  it,  cuts  the  perpendicular  of  the  front. 
The  demilune  face,  C"  P',  is  96  yards,  and  ranges  on  a  point 
D',  at  80  yards  from  the  point  H.  The  flank,  F'  E',  ranges 
on  a  point  at  2  yards  from  the  point  H,  and  is  terminated 
on  the  counterscarp  of  the  exterior  enceinte,  which  is 
drawn  from  a  point  P,  at  6  yards  from  0,  tangent  to  an  arc 
described  from  A,  with  a  radius  of  30  3'ards. 

248... The  salient  of  the  demilune  redoubt  is  at  46  yards 
from  the  point  0.  The  face  of  the  redoubt  is  36  yards, 
and  parallel  to  that  of  the  demilune  ;  its  flank,  G'  H',  is  also 
parallel  to  that  of  the  demilune. 

249. ..The  demilune  ditch  is  20  yards,  and  that  of  the 
redoubt  is  12  yards.  The  general  arrangement  of  the  cov- 
ered-way is  the  same  as  in  the  1st  Method. 

250. ..Profiles.  The  profiles  of  the  interior  enceinte 
and  of  the  demilune  redoubt  are  alike,  as  shown  on  CD"; 
and  those  of  the  counterguard  and  demilune  are  the  same 
as  shown  on  E"  F". 

251. ..The  parapets  of  the  towers  are  of  stone,  the  flanks 
being  pierced  with  two  embrasures.  The  flanks  of  the 
casemates  are  also  pierced  for  two  guns.  The. centre  of 
the  tower  is  occupied  l)y  a  stone  traverse.     The  casemated 


92  vauban's  third  method. 

flank,  Z  W,  is  pierced  for  only  one  trun  —  all  the  other 
defences  are  open. 

252... Remark.  The  plan  and  profiles  are  referred  to  a 
plane  of  comparison  taken  24  feet  below  the  liorizontal 
plane  of  site.  The  references  are  in  feet  and  fractional 
parts  of  feet.     Tlie  horizontal  distances  in  3'ards  and  feet. 

253. ..The  leading  idea  which  seems  to  have  governed 
Vauhan  in  the  dispositions  of  his  2d  and  3d  Methods,  Avas 
to  make  the  interior  enceinte  serve  as  a  general  retrench- 
ment with  covered  defences,  which  could  be  brought  into 
play  at  the  moment  wdien  an  attempt  was  made  to  pass  the 
interior  ditch  either  by  sap  or  openly.  Besides  this  promi- 
nent feature  of  the  2d  and  3d  Methods,  they  are  both  great 
improvements  on  the  1st  Method,  in  the  greater  dimensions 
given  to  the  counterguards  and  demilunes;  in  the  organi- 
zation of  the  latter  work  with  a  peniianent  though  small 
redoubt,  and  in  the  better  cover  aflbrded  to  the  masonry  of 
the  two  enceintes  and  the  outM'orks,  both  from  the  relative 
position  and  relief  of  these  elements.  This  last  purpose, 
however,  is  but  partially  efl:ected,  for  the  interior  enceinte, 
wdiich,  owing  to  the  small  flanks  given  to  the  demilune 
(which  last  have  but  a  slight  bearing  on  the  defence,  and, 
therefore,  might  have  been  omitted),  and  the  opening  be- 
tAveen  the  tenaille  and  counterguard  flanks  can  be  breached 
from  a  position  near  the  re-entering  place  of  arms,  and 
thus  be  exposed  to  assault  at  the  same  time  that  the  breach 
of  the  counterguard  is  attacked.  Besides  this  defect,  a 
great  part  of  the  scarp  wall  of  this  enceinte  in  rear  of  the 
tenaille  is  exposed  to  the  enemy's  view  over  the  tenaille,  as 
the  relief  of  this  work  has  to  be  so  far  reduced  that  the 
fire  of  the  counterguard  flank  can  be  brought  to  bear  on 
the  breacli  that  may  be  made  in  the  face  of  the  opposite 
counterguard. 

254... The  stone  towers  are  badly  contrived,  both  for 
strength  and  defence.  The  upper  platform,  surrounded  as 
it  is  with  a  stone  parapet,  and  having  a  traverse  of  the 
same  material  in  the  centre,  w^ould  be  a  perfect  slaughter- 
house under  a  heavy  fire  of  artillery  directed  against  it. 


vauban's  third  method,  93 

The  arches  of  the  casemates  are  inconvenientlj-  placed  for 
the  service  of  the  guns,  and,  liaving  the  exterior  walls  for 
one  of  their  abutments,  would  give  way  with  the  destruc- 
tion of  these  walls,  and  bring  down  all  the  superstructure 
by  their  fall. 

255... Besides  these  defects,  it  may  be  observed  that  the 
interior  enceinte  and  the  counterguards  have  the  same 
command,  which  would  be  found  greatly  to  the  disadvan- 
tage of  the  former  as  soon  as  the  enemy  has  succeeded  in 
gaining  possession  of  the  latter. 

256. ..The  low  revetcments  of  the  counterguard  and  the 
wide  berm  at  top,  would  subject  this  work  to  be  assaulted 
by  escalade  at  points  along  its  face  and  flanks  at  the  same 
time  that  an  assault  is  made  on  its  breach  ;  thus  paralyzing 
the  action  of  temporary  retrenchments  thrown  up  within 
this  work  to  protect  the  breach. 

257... It  was  owing,  probably,  to  these  obvious  defects, 
and  the  great  cost  of  the  bastioned  towers,  that  Cormon- 
taingne,  who,  in  his  writings,  professes  to  follow  out  the 
leading  ideas  of  Yauban,  selected  the  main  features  of  his 
1st  Method  rather  than  those  of  his  2d  and  3d,  in  the 
bastioned  front  which  has  received  his  name.  Although 
impci-fectly  devised,  both  as  to  plan  and  construction,  the 
3d  Method  of  Yauban  presents  more  elements  of  resistance 
than  Cormontaingne's  front ;  and,  with  suitable  modifica- 
tions of  the  interior  enceinte  and  the  demilune  to  remedy 
the  defects  which  have  been  pointed  out,  and  by  increasing 
the  dimensions  of  the  interior  enceinte  so  as  to  afford  good- 
sized  bastions,  with  strong  flanking  dispositions,  it  would 
offer  far  superior  defensive  means  than  it  now  possesses. 


94  coumoxtaixgxe's  method. 


a|ormont;iin()iie*.s  |tlclho(l 


258...Cormontaingiie,  the  immediate  successor  of  Vau- 
ban,  holds  a  place  only  second  to  this  master  of  tlie  art 
in  the  estimation  of  the  engineers  of  the  French  school. 
Cormontaingne,  who  to  superior  abilities  united  a  wide 
range  of  experience,  both  in  the  c(Mislruction  and  in  the 
attack  of  permanent  works,  studied  with  great  care  the 
results  of  A'auban's  immense  labors.  In  working  out  the 
front  which  has  received  his  name,  Coi-montaingne  seems 
to  have  api)lied  himself  rather  to  remedy  the  defects  no- 
ticeable in  the  methods  of  Vauban,  than  to  produce  any 
radical  change  in  the  combinations  which  had  thus  far 
received  the  sanction  of  engineers  generally.  lie  was  thus 
led  to  reject  the  Ist  and  2d  Methods  of  Vauban  from  the 
defects  wiruli  have  been  noticed,  and  also  from  the  increased 
cost  of  constructing  the  bastioned  towers,  and  to  take  the 
1st  Method  as  the  basis  of  his  own  changes. 

25i(...Coniiontaingne  was  the  first  to  devcloj)  i-learly  the 
influence  ol'  large  demilunes  on  the  })rogress  of  the  attack, 
by  their  foiining  deep  re-cntcrings  between  them  in  front 
of  the  bastion  salients,  and  also  the  increased  strength  gained 
by  fortifying  on  a  right  line,  or  on  polygons  with  a  great 
number  of  sides,  as  in  both  of  these  cases  the  fronts  assailed 
cannot  be  enveloped  by  the  assailant's  works,  and  the  demi- 
lunes from  their  salient  position  intercept  the  prolongations 
of  the  bastion  faces,  and  thus  mask  them  from  the  positions 
tVom  which  alone  an  eutilading  fire  could  be  brought  upon 
tlu'iii.  Besides  this,  Cormontaingne  lays  down  as  a  prin- 
ciple, that  )io  masonrji  shall  be  exi)Osed  to  tJte  distant  batteries 
of  the  assailant ;  and  to  obtain  this  point  he  has  so  arranged 
the  height  of  his  principal  scarps,  and  the  command  given 
to  the  glacis  crest  in  front  of  them,  that  the  toj)  of  the 
scarp  shall  not  lie  above  the  level  of  this  crest,  thus  mask- 


cormontaingne's  method.  95 

ing  tlie  entire  scarp,  by  the  earth  forming  the  glacis,  from 
all  positions  in  advance  of  the  glacis  crest. 

His  modifications  of  the  plan  and  profile  of  Vauban's  1st 
Method,  chiefly  resnlt  from  the  above  as  a  basis. 

260. ..Enceinte.  The  modifications  of  Vauban's  tra^c,  Fig. 
4,  PI.  1,  are  difierent  in  the  various  works  of  Cormontaingnc* 
but  the  following  he  indicates  in  his  memoirs  as  the  most 
perfect.  The  exterior  side  is  360  yards ;  the  perpendicular 
I- ;  the  faces  of  the  bastions  J  of  the  exterior  side ;  the 
flanks  are  40  yards,  and  are  so  placed  that  the  curtain  shall 
be  120  yards:  this  combination  makes  the  lines  of  defence 
somewhat  less,  and  the  bastions  somewhat  smaller,  than  in 
Vauban's  method. 

261. ..The  dimensions  of  the  enceinte  ditch  are  so  regu- 
lated by  Cormontaingne  as  to  furnish  earth  sutficicnt  for 
the  embankments.  It  is  28  yards  wide  at  the  salient,  and 
from  2  to  4  yards  wider  o])])osite  the  tcnailic;  this  admits 
the  entire  fire  of  the  flanks  to -sweep  the  ditch. 

262...TENATLLE.  The  tenaille  is  made  with  a  curtain  and 
wings;  a  ditch  10  yards  wide  being  left  between  it,  the 
curtain  and  the  flanks. 

263... Demilune.  Cormontaingne  placed  little  value  on 
small  demihines,  as  they  form  but  slight  and,  therefore, 
weak  re-enterings  before  the  bastions,  and,  consequently, 
retard  but  little  the  enemy's  attack  upon  the  bastions; 
besides  this,  a  small  demilune  covers  but  very  imperfectly 
the  shoulder  angles  of  the  bastions.  To  remedy  these 
defects,  his  demilune  is  so  laid  out  that  the  prolongations 
of  the  magistrals  of  its  faces  will  intersect  the  bastion  faces 
at  30  yards  from  the  shoulder  angles ;  the  lengths  of  its 
faces  being  120  yards. 

264... By  thus  enlarging  the  demilune,  sufiicient  space  is 
gained  to  place  a  strong  redoubt  in  its  interior.  The  de- 
fence of  the  demilune  may  be  made  with  more  obstinacy, 
fi*om  the  support  it  receives  from  the  redoubt;  and  the 
enemy  will  be  obliged  to  carry  the  redoubt  before  he  can 
assault  the  breach  he  may  have  made  in  the  bastion  face, 
as  this  breach  is  seen  in  reverse  by  the  fire  of  the  flanks  of 
the  redoubt. 


96  curmontaixgne's  method. 

265. ..Demilune  Reduit.  To  circumscnbc  as  much  as 
practicable  the  space  in  the  deniihme  wliich  the  enemy, 
after  he  gains  it,  requires  for  his  works,  the  extremity  of 
the  (lemihme  terreplein,  wliich  is  also  the  top  of  the 
counterscarp  of  the  redoubt,  is  drawn  at  20  yards  from  the 
magistral  of  the  face;  the  ditch  of  the  redoubt  is  10  yards 
wide,  and  the  nuigistral  of  its  face  is  parallel  with  the 
counterscarp.  By  this  arrangement  the  ditch  of  the  redoubt 
is  well  flanked  by  the  face  of  the  bastion  near  the  shoulder 
angle.  To  la}^  out  the  flanks  of  the  redoubt,  the  counter- 
scarps of  the  enceinte  are  prolonged  to  intersect  the  per- 
pendicular of  the  front;  from  this  point  of  intersection  a 
distance  of  20  yards  is  set  off  along  each  counterscarp,  the 
two  points  thus  obtained  are  joined  by  a  right  line,  which  is 
the  gorge  of  the  redoubt;  from  the  extremities  of  the  gorge 
two  lines  are  drawn  parallel  to  the  capital  of  the  demilune, 
these  lines  limit  the  terreplein  of  the  flanks;  the  magistrals 
of  the  flanks  are  drawn  parallel  to  and  at  16  yards  from  the 
last  lines.  The  ditch  of  the  demilune  is  20  yards  wide; 
its  depth  is  the  same  as  that  of  the  enceinte. 

266...  Covered -WAY,  etc.  The  general  width  of  the  cov- 
ered-Avay  is  10  yards.  Cormontaingne  enlarged  consid- 
erably the  re-entering  place  of  arms,  to  Avhich  he  added 
a  redoubt  with  a  revetted  scarp  and  counterscarp.  The 
addition  of  this  redoubt  is  a  great  improvement  upon  the 
covered-way  of  Vauban,  who  indicates  in  his  works  small 
redoubts  of  earth,  or  tambours  of  wood,  for  the  same  pur- 
pose. Cormontaingne's  redoubt  increases  the  strength  of 
the  covered-way ;  the  troops  assembled  in  the  covered-way, 
for  sorties,  are  secure  under  its  fires;  it  sees  in  reverse,  and 
protects  any  breach  made  in  the  face  of  the  demilune; 
finally,  it  serves,  in  connection  with  the  extremity  of  the 
demilune,  to  cover  the  opening  left  between  the  flanks  of 
the  bastion  and  the  wings  of  the  tenaille,  tlirough  which, 
if  a  breach  was  made  in  the  curtain,  the  interior  retrench- 
ments, resting  upon  either  the  flanks  or  faces  of  the  bastion, 
could  be  turned, 

267. ..To  lay  out  the  interior  crests  of  the   re-entering 


cormontaingne's  method.  97 

place  of  arms,  two  points  are  taken  on  the  counlerscarps  of 
the  bastion  and  deniihine,  at  54  yards  from  their  })()int  of 
intersection;  from  tliese  points  as  centres,  with  radii  of  60 
yards,  arcs  are  described,  wliose  intcrsectiori,  joined  with 
the  centres,  gives  tlie  direction  of  tlie  faces.  The  magistral 
of  its  redoubt  is  found  by  a  similai*  construction  ;  distances 
of  40  yards  being  set  oti"  ahmg  tlie  counterscarps,  and  the 
faces  being  drawn  from  these  points  so  as  to  be  86  yards 
long.  The  ditch  of  the  redoubt  is  5  yards  wide  and  2.1 
yards  deep. 

268. ..Traverses  are  placed  along  tlie  covered-way,  to 
close  the  places  of  arms,  defend  the  covered-way,  and  inter- 
cept projectiles  fired  in  ricochet. 

269... The  crest  of  the  glacis  is  broken  into  a  cremaillere 
line,  to  allow  room  for  the  deliles  of  the  traverses.  The 
short  branches  of  the  cremaillere  throw  a  lire  on  the  sali- 
ents of  the  covered-way;  the  positions  of  the  long  branches 
are  so  taken  that  the  deiilcs  may  be  seen  and  swept  by  the 
fire  of  the  works  in  their  rear. 

270...PiioFiLES.  Cormontaingne,  after  a  series  of  trials, 
whose  object  was  to  give  the  ditches  such  dimensions  that 
they  should  furnish  the  earth  required  for  the  embank- 
ments, regulated  the  command  of  the  different  works  as 
follows.  The  lowest  work,  which  is  the  demilune  covered- 
way,  he  lays  down  as  a  rule,  shall  command  the  exterior 
ground  by  not  less  than  7|  feet ;  and  the  works  most  ad- 
vanced shall  be  commanded  by  those  in  their  rear. 

271. ..It  was  found  that,  for  the  purpose  of  equalizing  the 
excavations  and  embankments  of  the  front,  the  crest  of  the 
deniihine  covcrcd-way  should  have  a  command  of  10}  feet 
above  the  natural  ground.  The  crest  of  the  l>astion  covered- 
way,  and  of  tlie  re-entering  [)lace  of  arms,  command  the 
crest  of  the  demilune  covered-way  by  2  feet.  The  niagi-^tral 
of  the  enceinte  is  horiz.ontal,  its  elevation  being  the  same 
as  the  mean  elevation  of  the  crest  of  the  bastion  covered- 
way.  The  salient  of  the  bastion  commands  its  covered-way 
by  8  feet.  The  total  height  of  the  scarp  is  80  feet.  This 
dimension  has  since  been  generally  adopted  by  engineers — 
7 


98  cormontaixgne's  mktiiod. 

a  wall  of  tills  lioiglit  opposing  a  sufficient  ohstaolo  to  an 
attempt  at  escalade.  Tlie  absolute  relief  of  the  flanks  is 
thus  made  37i  feet;  with  this  relief  a  piece,  tiring  under  a 
depression  of  I  through  an  embrasure  in  the  tiank,  imd  in 
the  direction  of  the  curtain,  will  strike  the  bottom  of  the 
ditch  at  the  middle  point  of  the  curtain;  so  that  were  the 
relief  increased,  the  length  of  curtain  remaining  the  same, 
the  ditch  would  no  longer  be  thorouglily  flanked. 

272. ..The  relief  of  tlie  tenaillo  is  determined  as  in  Yau- 
ban's  Method,  so  as  not  to  mask  the  tire  of  the  flanks  ni>on 
the  ditch  opposite  the  extremity  of  the  demilune,  as  it  is 
here  that  a  breach  may  be  made  in  the  bastion  face  through 
the  ditch  of  the  demilune. 

273. .The  demilune  is  commanded  by  the  enceinte,  3  feet, 
and  by  its  own  redoubt,  1|  feet;  the  demilune,  therefore, 
commands  its  covered-way,  7  feet,  which  is  more  than  is 
indispensably  requisite;  for  an  enemy,  standing  on  the  crest 
of  tlie  covered-wa}",  cannot  have  a  plunging  tire  into  a  work 
in  the  rear  of  it  if  the  latter  commands  the  crest  by  5  feet. 

274... The  redoubt  of  the  re-entering  place  of  arms  com- 
mands the  crest  of  the  glacis  only  4h  feet;  its  interior  crest 
is  so  [)laced  as  not  to  mask  the  tire  of  the  bastion  faces  on 
the  glacis  in  advance  of  it. 

275... The  interior  crests  of  all  the  works  are  7^  feet  above 
their  terreplein,  except  that  of  the  tenaille,  wliich  is  Gh  feet, 
and  of  the  redoubt  of  the  re-entering  place  of  arms,  which 
is  9  feet.  The  interior  crests  of  the  faces  of  all  the  works 
exposed  to  entilading  fires  are  one  foot  higher  at  the  sali- 
ents than  at  the  extremities. 

276. ..The  profile  of  the  parapet  of  the  princi})al  outworks 
is  the  same  as  that  of  the  enceinte. 

277. ..(communications.  The  communication.^^  are  gener- 
ally of  the  same  nature,  and  placed  about  in  the  same  posi- 
tions, as  in  Vauban's  Method. 

278. ..Glacis.  The  planes  of  the  glacis  are  so  determined 
that  they  may  be  swept  by  the  fire  of  the  works  in  the  rear; 
their  inclination  is  usualh'  about  twenty-four  base  to  one 
altitude. 


C0KM0NTATNG^'K'8    METHOD.  99 

279. ..Interior  Retrenchments.  Cormoiituingno  indicates 
tlie  gorge  and  shoulders  of  the  hastion  as  the  position  for  an 
interior  retrenchment,  when  this  addition  to  the  front  is 
Tnade  solely  with  a  view  of  disputing  the  breach  in  the  bas- 
tion and  its  interior  with  the  assailant.  In  this  case  he 
gives  the  retrenchment  the  form  of  a  tenaille,  or  a  bas- 
tioiK'd  front,  resting  it  either  upon  the  shoulder  angles  ot 
the  bastion,  or  u}>on  the  tv.-o  adjacent  curtains,  on  })()ints 
beyond  the  prolongation  of  the  ditch  between  tlie  tenailles 
and  the  flanks,  and  in  this  i)osition  he  gives  it  the  form  of 
a  bastioned  front. 

In  the  former  case,  the  portion  of  the  interior  of  the  bas- 
tions between  the  flanks  is  preserved  for  the  defence,  but 
the  retrenchment  is  liable  to  be  turned,  by  a  breach  nuide 
in  tlie  flank,  or  in  the  portion  of  the  curtain  where  it  joins 
the  flank.  In  the  latter  case,  a  breach  in  the  bastion  jilaces 
the  whole  of  the  interior  within  view  of  the  assailant,  but 
the  retrenchment  itself  is  secure  from  its  position  from 
being  turned,  as  a  breach  in  the  curtain  cannot  be  made  in 
rear  of  it. 

2(S0...Cavalter.  AVhen  a  greater  command  of  the  site 
than  that  aftbrded  by  the  enceinte  is  requisite  on  any  front, 
Cormontaingne  jtlaces  a  cavalier  within  the  bastion.  To 
this  work  he  gives  the  same  form  as  that  of  the  bastion, 
]>lacing  the  faces  and  flanks  of  the  two  parallel  to  each 
other.  The  faces  of  the  cavalier  are  alone  revetted,  as  well 
as  the  counterscarp  of  their  ditch  wliidi  is  cut  within  the 
bastion.  This  ditch  is  broken  oft  at  the  shoulder  angles  of 
the  cavalier  and  directed  upon  the  faces,  these  [tortious  also 
having  a  revetted  scarji  and  counterscarp.  A  parapet  is 
thi-own  up  behind  the  scaip  and  between  the  flank  of  the 
cavalier  and  the  ])astion  faces,  thus  isolating  the  anterior 
portion  of  the  bastion,  and  furnishing  an  interior  retrench- 
ment which,  when  the  shoulders  ami  flanks  of  the  bastions 
are  masked  from  the  assailant's  view,  can  only  be  carried 
by  a  bleach  made  either  in  the  cavalier  face  or  in  the  \h)v- 
tions  resting  on  the  cavalier  and  l)astion  faces. 

2S1  ...Remarks.     From  the  preceding  description,  it  ap- 


100  CORMOXTAIXfJXE'S     METHOD. 

pears  that  the  most  important  modification  made  hy  Cor- 
montaingne,  in  Vanban's  1st  Method,  consists  in  the  means 
taken  to  cover  the  masovry  from  distant  batteries ;  capa- 
cious bastions,  susceptible  of  receiving  efficient  permanent 
ititerior  retrencliments ;  an  enlarged  drmiboie,  which  places 
the  bastions  in  strong  re-entorings,  covers  the  shoulder 
angles,  and  admits  of  a  rcdovht  in  its  interior,  which  work 
strengthens  the  demilune,  and  sees  in  reverse  the  breach 
made  in  the  bastion  face;  an  enlarged  re-entering  })lace  of 
arms,  containing  a  redoubt,  which  strengthens  the  entire 
covered-way,  and  covers  the  movement  of  the  troops  in 
sorties. 

2H2... These  modifications,  although  of  great  value,  and 
constituting  an  important  step  in  the  art,  still  leave  much 
to  be  desired ;  and  engineers,  since  Cormontaingne's  time, 
have  sought  to  remedy  the  defects  of  his  method,  of  which 
the  following  are  the  principal.  The  enceinte  has  rather 
too  slight  a  command,  and  is  without  any  bomb-proof 
shelters :  the  inclination  of  the  superior  slope  of  its  para- 
pet, which  is  ^,  is  too  small  to  have  the  ditches  well 
flanked;  a  breach  can  be  made  in  the  bastion  ftice  through 
the  ditch  of  the  demilune;  there  are  dead  spaces  in  the 
ditch  of  the  demilune  near  the  extremities  of  its  faces;  the 
redoubt  of  the  re-entering  place  of  arms  is  not  tenable  after 
the  demilune  is  taken  ;  the  traverses  of  the  covered-way  do 
not  afford  the  requisite  protection  to  that  work;  finally, 
communications  are  mostly  inconvenient,  and  not  well 
covered   from   the   assailant's  fires. 


METHODS  OF  THE  t^CIIOOLS  OF  MEZIERES  AND  METZ.         101 


Hcihodfi  01  the  Schools  of  ^llc^ierrfi  and  ^W&d. 


283. ..The  School  of  Application  for  engineer  and  artil- 
lery officers,  first  cstahlished  at  Mezicres  and  subsequently 
at  Metz,  has  given  to  France,  from  about  the  period  of  the 
Frencli  devolution  down  to  the  present  day,  the  far  greater 
portion  of  the  many  able  officers  who  have  gained  such 
universal  and  deserved  celebrity  for  these  two  corps. 

284... lu  these  schools  the  precepts  of  Yauban  and  Cor- 
montaingne  have  been  jealously  guarded  as  the  highest 
authoi-ity,  and  their  manuscripts  and  published  works  have 
formed  the  basis  of  the  instruction  given  in  them. 

28,5... Some  slight  modifications  were  proposed  in  the 
front  of  Cormontaingne  by  two  engineers,  Chatillov  and 
Duvigneau^  and  taught  ])y  them  in  the  course  of  permanent 
fortification  given  in  the  school.  These  changes  chiefly 
consisted  in  enlarging  the  demilune  and  making  it  more 
salient;  and  in  jdacing  in  the  flanks  of  its  redoubt  case- 
mates for  cannon,  with  reverse  views  on  the  breaches  that 
miglit  be  made  in  the  bastion  faces. 

280. ..The  teaching  of  the  school  of  Metz  has  received  its 
principal  impress  from  General  Noizet,  himself  a  pupil  of 
General  Ilaxo,  regarded  as  the  first  among  the  successors 
of  Vauban  and  Cormontaingne,  who,  for  several  years, 
whilst  a  captain  of  engineei's,  performed  the  functions  of 
professor  of  fortification,  and  who  has  recently  given  to 
the  pii])lic  the  results  of  his  lectures  delivered  in  the 
school. 

287. ..The  front,  which  for  some  years  back  and  up  to 
the  [)resent  time,  has  been  taught  in  this  school,  goes  by 
the  apjiellation  of  Noizct's  Mcih<j<i.  In  it  there  is  no  sensi- 
ble departure  from  the  views  and  methods  of  Vauban  and 
Cormontaingne;  the  object  l)eing  to  introduce  such  modifi- 
cations into  the  front  of  the  latter  as  would  remedy  some 


102  xoizet's  method. 

of  its  acknowlodged  defects.  In  doiiicr  this,  aiiotlior  object 
was  kept  in  view,  wliicli  was  to  present  in  tlie  conihinu- 
tions  of  this  front  a  problem,  in  the  sohition  of  whicli  llie 
pnpil  would  be  called  ui)on  to  ap[>I_v  both  the  elementary 
principles  of  fortification  and  the  geometrical  methods  that 
the  engineer  has  to  use  as  his  princii)al  tool  in  such  prob- 
lems to  a  special  case,  that  of  a  front  adopted  to  a  horizontal 
site.  It  is  in  this  point  of  view  that  the  analysis  and  con- 
struction of  tliis  front  liave  been  adopted  as  the  basis  for 
the  elementary  instruction  given  in  permanent  fortification 
in  this  institution. 


foiscffi  Pcthol 


288. ..General  Requirements.  Noizet,  in  his  front, 
takes  as  the  basis  of  the  construction  of  the  enceinte,  the 
length  of  the  exterior  side  and  the  command;  assuming 
these  within  the  limits  laid  down  b}'  Vauban  and  Cormon- 
taingne;  and  in  the  combinations  of  outworks  with  the 
enceinte,  following  the  latter  engineer;  introducing  only 
such  modifications  as  seem  to  best  fulfil  tlic  general  condi- 
tions of  the  problem,  which  are  as  follows: 

Ist.  The  enceinte  must  be  secure  from  a  surprise  by 
escalade;  present  an  unbroken  line  on  every  side  by 
wliich  it  can  be  approached  by  the  assailant;  and  have  its 
scarp  thoroughly  swept  by  fire  from  within  the  enceinte. 

2d.  The  parapets  of  the  enceinte  and  outworks  must  be 
proof  against  projectiles  of  the  heaviest  calibre. 

3d.  The  scarp  walls  of  the  enceinte  and  outworks  must 
be  masked  from  all  positions  that  can  be  taken  up  by  the 
assailant  for  his  breaching  batteries  beyond  the  crest  of  the 
glacis. 

4th.  The  fianking  dispositions,  both  of  the  enceinte  and 


noizet's  method.  103 

outworks,  must  be  adapted  to  the  range  of  small  anus 
witliiu  accurate  liuiits. 

5tli.  The  comnuiud  of"  the  enceinte  must  be  so  regulated 
as  to  overlook  all  the  outworks  aud  bring  their  interior, 
their  ditches,  the  glacis  and  the  site  beyond  it  thoroughly 
under  fire  of  both  artillery  and  small  arms. 

6th.  The  command  of  the  outworks  must  be  so  combined 
that  the  more  advanced  shall  be  commanded  by  the  more 
retired ;  and,  when  this  cannot  be  effected,  the  retired  one, 
which  is  eonuuanded  by  an  advanced  one,  must  have  its 
interior  detiled  from  the  latter. 

Ttli.  The  outworks  must  be  so  combined  that  they  sViall 
fall  into  the  possession  of  the  assailant  in  succession,  from 
the  more  advanced  to  the  more  retired ;  and  the  more  im- 
portant ones  should  receive  a  sufficient  height  of  scarp  wall 
to  secure  them  from  being  entered  hy  a  sudden  rush  of  the 
enemy. 

8th.  There  must  be  a  sufficiency  of  the  various  kinds  of 
communications  to  admit  of  a  prompt  circulation,  both 
within  the  enceinte  and  to  the  exterior,  for  the  ordinary 
service  of  the  garrison  and  for  sorties  against  the  assailant. 

289. ..General  Data  of  the  Enceinte.  In  the  following 
description  and  analysis  of  the  front  of  Xoizet,  the  plane  of 
comparison  is  assumed  at  60  feet  below  the  horizontal  plane 
of  site,  the  reference  of  which  will  be,  therefore,  (60,0). 
The  yard  is  taken  as  the  unit  for  the  horizontal  dimensions 
of  the  plan  ;  and  the  foot  as  the  unit  tor  the  lefei'ences  and 
vertical  dimensions. 

Converting  the  French  measures  into  their  equivalent 
English  units,  the  exterior  side  of  the  front  is  380  yards; 
the  height  of  the  scarp  wall,  33  feet;  the  command  of  the 
interior  crest  of  the  curtain  o\'er  the  plane  of  site,  21  feet; 
and  its  height  above  the  magistral,  13  feet. 

290...rROFiLE  OF  Enceinte.  PI.  2,  Fig.  4.  The  profile 
of  the  enceinte  here  given  is  similar  to  that  of  Cormon- 
taingne,  and  was  adopted  by  subsecpient  engineers  until 
the  more  recently  modified  one  already  described.  Its 
slopes  and    dimensions    are   as   follows:      The    searp   and 


104  noizet's  method. 

counterscarp  slopes,  Y?  ^^^'  <^"^  ^''^^c  to  twenty  altitude. 
Exterior  slope,  j,  or  45°.  Superior  slope,  ^.  Interior 
slope,  f.  Banquette-slope,  J.  Kanipart-slope,  |.  Terre- 
pleins  8  feet  below  the  interior  crests.  Berm,  2  feet. 
Distance  between  the  magistral  and  foot  of  the  exterior 
slope,  1.5  feet.  Thickness  of  parapet,  20  feet.  Height  of 
interior  crest  above  the  banquette-tread,  4.5  feet.  Ban- 
quette-tread, 4.5  feet.  General  width  of  terrcplein,  esti- 
mated from  the  vertical  through  the  interior  crest,  48  feet. 

291... Magistral  of  the  Curtail.  The  length  of  this  is 
determined  bv  the  condition  that,  the  artillery  tire  from  the 
flanks,  under  the  de[)ression  of  ^,  shall  attain  a  point  at  1.5 
feet  above  the  bottom  of  the  ditch,  at  the  centre  of  the 
curtain  ;  the  bottom  of  the  ditch  itself,  at  the  centre,  being, 
for  the  purposes  of  drainage,  1.5  feet  higher  than  at  the 
extremities  of  the  curtain,  thus  giving  to  the  scarp  a  height 
of  31.50  feet  at  the  centre,  instead  of  83  feet,  the  general 
height  throughout  the  enceinte. 

Sup])0sing,  now,  a  section,  PI.  2,  Figs.  2,  4,  to  be  made 
through  the  flanks  by  a  vertical  plane  passed  through  the 
foot  of  the  curtain  scarp,  and  that  a  line  be  drawn  in  it, 
paniUel  to  the  superior  slope  and  at  3  feet  below  it,  to 
represent  the  direction  of  the  artillery  Are,  this  line  must 
attain  the  point  at  1.5  feet  above  the  bottom  of  the  ditch, 
at  the  centre  of  the  curtain,  to  fulfll  the  required  condition 
of  a  thorough  flanking  disposition  throughout  the  entire 
extent  of  the  enceinte.  If,  then,  a  horizontal  line  be  drawn 
from  the  })oint  to  be  attained  to  intersect  the  vertical 
through  the  interior  crest,  it  will  be  the  horizontal  distance 
l)etween  the  interior  crest  and  the  centre  of  tlie  curtain, 
and,  fron)  the  construction,  will  be  equal  to  six  times  the 
perpendicular  distance  intercepted  between  it  and  the  line 
of  artillery  fir(^ 

Now,  from  the  above  there  is  given  to  calculate  this  base 
the  entire  height  of  the  interior  crest,  above  the  bottom  of 
the  ditch,  44.50  feet;  the  height  of  the  same  point  above 
the  line  of  artillery  fire,  3  feet;  and  the  height  of  the  point 
to  be  attained  above  the  bottom  of  the  ditch,  1.5  i'cct.     The 


noizet's  method.  105 

distance  sought,  therefore,  will  he  0(44.50  ft.  —  4.50  ft.)= 
240  ft. 

To  obtain  the  leui^th  of  the  magistral  corresponding  to 
tliis  distance,  it  will  only  be  requisite  to  subtract  from  it  the 
horizontal  distance  between  the  interior  crest  and  the  point 
of  the  section  corresponding  to  the  magistral  of  the  flank. 
This  last  distance  is  com})osed  of  the  thickness  of  the 
para})et,  the  base  of  the  exterior  slope,  and  the  lierm. 
The  tirst  is  20  feet.  The  second  is  found  by  taking  from 
the  height  of  the  interior  crest,  above  the  magistral,  which 
is  13  feet,  one-sixtli  tlie  thickness  of  the  jiarapet,  or  3.33 
feet,  which  gives  13  ft.  — 3.33  ft.=^9.66  feet.  The  third  is 
1.50  feet.  The  required  distance,  therefore,  is  240  ft. — 
(20  ft.+9.G6  ft.+1.50  ft.)=208.84  feet,  or  60.61  yards. 

292... Magistral  of  Enceinte.  T\.  2,  Fig.  5.  Having 
found  the  length  of  the  magistral  of  the  curtain,  the  pro- 
jection of  the  magistral  of  the  enceinte  on  the  plane  of 
reference  is  determined  as  follows:  Draw  a  line  for  the 
exterior  side,  and  set  oft"  on  it  A  B—S80  yards;  bisect  this 
distance  by  a  perpendicular,  on  which  set  off  CD=^l  A  B= 
(53.33  yards;  from  A  and  B  draw  lines  thi'ough  D,  these 
are  the  directions  of  the  faces  and  lines  of  defence;  draw  a 
]iai-al]el  to  CD,  on  each  side  of  it,  and  at  69.61  yards,  the 
length  of  the  half  curtain,  from  it,  join  the  points  G  and  JI 
where  these  ])arallels  intersect  the  lines  AD  and  BD  pro- 
longed ;  G  II  is  the  position  of  the  curtain  ;  G  B  and  II A 
the  lines  of  defence;  from  G  and  //draw  a  line,  making 
ail  angle  \  with  the  perpendicular,  to  the  curtain  at  each  of 
these  points,  the  parts  G  E  -Awd  F II  of  these  last  lines  are 
the  flanks  ;  and  A  E  and  B  F  the  faces. 

293. ..The  position  of  the  magistral  with  resjtcct  to  the 
plane  of  reference  is  determined  as  follows  :  The  magistral 
of  the  curtain  is  lioiizoiital.  As  it  is  13  feet  below  tlie  inte- 
rior crest,  and  this  line  is  placed  at  21  feet  aliove  the  jilane 
of  site,  the  magistral  is  8  feet  above  this  plane,  and,  there- 
fore, from  the  jjosition  given  the  plane  of  comparison,  68 
feet  above  this  last  plane ;  its  reference,  therefore,  is  (68.0) 
The  flank  is  1.5  feet  lower  at  the  shoulder  than  at  the  cur- 


106  noizet's  method. 

tJiin  angle,  the  reference  of  tlie  shoulder  is,  then,  (66.50). 
The  face  is  horizontal,  and  its  reference  also  (66.50.) 

294. ..Manner  of  determining  the  position  of  a  point  of 
THE  Interior  Crest.  To  determine  the  projection  of  a 
point  of  the  interior  crest  contained  in  a  profile  plane,  the 
height  of  the  point  above  the  magistral  being  known,  we 
first  subtract  from  this  height  ^  the  thickness  of  the  para- 
pet, the  remainder  will  be  the  height  of  the  exterior  crest 
above  the  magistral,  and,  when  the  exterior  slope  is  J,  will 
also  be  the  base  of  the  slope  ;  adding  together  the  thick- 
ness of  the  parapet,  the  base  of  the  exterior  slope  as  just 
determined,  and  the  distance  from  the  foot  of  the  exterior 
slope  to  the  magistral,  the  sum  will  be  the  horizontal  dis- 
tance between  the  magistral  and  interior  crest,  or  the 
distance  to  be  set  oft',  along  the  trace  of  the  profile  plane, 
from  the  magistral,  to  obtain  the  projection  of  the  re(piired 
point  of  the  interior  crest. 

295. ..Interior  Crest  of  the  Enceinte.  PI.  2,  Fig.  6. 
The  position  of  the  interior  crest  above  the  magistral  is 
fixed  as  follows  :  That  of  the  curtain  is  })arallcl  to  the 
magistral,  and  13  feet  above  it.  Those  of  the  flanks  and 
faces  of  the  bastiou  are  contained  in  the  same  plane,  the 
scale  of  declivity  of  which  is  taken  parallel  to  the  bastion 
capital.  The  position  of  this  plane  is  determined  by  plac- 
ing its  horizontal,  which  coincides  with  a  pancoupe  4.30 
yards  in  length  at  the  bastion  salient,  at  4.50  feet  above  the 
horizontal  drawn  through  the  points  where  the  flanks  join 
the  curtain. 

The  reference  of  the  interior  crest  of  the  curtain  from 
the  above  data  will,  therefore,  be  (81.0);  and  the  horizontal 
distance  of  any  point  of  it  from  the  magistral  31.16  feet, 
or  10.38  yards,  as  these  two  lines  are  parallel. 

Having  drawn  the  projection  of  the  interior  crest  of  the 
curtain,  the  })oint  where  it  joins  the  flank  may  be  deter- 
mined approximately',  and  with  sufficient  accuracy,  by  bi- 
secting the  curtain  angle  of  the  magistrals,  and  taking  the 
point,  where  the  bisecting  line  cuts  the  interior  crest,  as 
the  extremity  of  the  flank.     From  this  point,  of  which  the 


noizet's  method.  107 

reference  is  (81.0),  if  a  line  he  drawn  perpemlienlar  to  the 
l)asti()n  capital  it  will  l)e  horizontal  (81.0)  of  the  })lane  of 
the  interior  crests  of  the  bastion  ;  that  at  tlie  pancoupe  is 
4.50  feet  higlier,  and  its  reference  will,  therefore,  be  (85.50). 
To  find  the  position  of  this  last  horizontal,  which  is  also 
that  of  the  pancoupe,  draw  two  lines  parallel  to  the  bastion 
capital,  and  2.15  yards  from  it,  they  will  limit  the  pancoupe. 
Now,  as  the  extremity  of  the  pancoupe  is  a  point  of  the 
interior  crest  of  t]ie  bastion  face,  and  its  reference  is  (85.50), 
the  height  of  this  point  above  the  magistral  is  19  feet,  as 
the  reference  of  this  last  line  is  (6(3.50).  The  horizontal 
distance,  therefore,  from  this  point  to  the  magistral  is 
(20  ft. +15.66  ft.+1.50  ft.)-^37.16  ft.=12.38  yds.  Drawing 
a  parallel,  therefore,  to  the  magistral  of  the  face,  and  at 
12.38  yards  from  it,  the  point  where  it  cuts  the  parallel  to 
the  capital,  at  2.15  yards  from  it,  will  be  the  required  point, 
through  which  the  horizontal  (85.50)  is  drawn. 

Having  two  horizontals  of  the  plane,  its  scale  of  declivity 
can  be  constructed,  and  other  horizontals  be  determined. 
The  jirojeetion  of  the  })()int  of  the  interior  crest  of  the  face 
on  any  given  horizontal,  can  l)e  found  by  the  same  process 
as  the  one  just  described.  For  example,  take  the  horizon- 
tal, (84.0) ;  the  perpendicular  distance  of  the  point  on  it 
from  the  magistral  is  (20  ft. +  14.16  ft.  +  1.50  ft.)^  35.66  ft.  or 
11.88  yds.  The  two  points  thus  determined  being  joined, 
will  give  the  projection  of  the  interior  crest  of  the  face. 

To  find  that  of  the  flank,  of  which  one  point,  (81.0),  lias 
been  found,  bisect  the  shoulder  angle  of  the  magistral,  the 
point  wliere  the  bisecting  line  cuts  the  interior  crest  of  the 
face  will  give,  approximately,  the  other  extremity  of  the  line 
required. 

The  constructions  for  the  interior  crests,  just  given,  are 
only  approximations  to  a  true  result;  as  the  horizontal  dis- 
tances calculated,  l)eing  those  contained  in  ])r()file  j)lanes, 
ought  to  have  been  set  oft'  perpendicular  to  tlie  iirojection 
of  the  interior  crest ;  but  the  ditterence  between  the  results 
of  this  approxinuite  method  and  one  rigorously  accurate 
will,  in  the  present  case,  be  so  small,  owing  to  the  slight 


108  noizet's  method. 

divergence  between  the  projections  of  the  magistral  and 
interior  crest  of  tlie  face,  as  not  to  aftect,  in  any  apprecia- 
ble degree,  the  real  positions  of  the  required  points.  The 
same  remarks  are  a}»})lical)]e  to  the  constructions  for  find- 
ing the  extremities  of  the  iiank. 

29G...rAi{APET  OF  Enceinte.  Having  drawn  the  interior 
crest  of  the  enceinte,  all  the  other  lines  of  the  parapet — 
except  the  foot  of  the  exterior  slope — and  the  inward  line 
of  the  terreplein  are  drawn  parallel  to  it.  The  foot  of  the 
exterior  slope  is  drawn  parallel  to  the  magistral. 

Terreplein  of  Enceinte.  PI.  2,  Fig.  6.  The  terrepleins 
of  the  faces  and  flanks  are  in  a  plane  parallel  to  that  of 
their  interior  crest  and  8  feet  below  it,  estimated  vertically. 
To  find  the  reference  of  an}-  horizontal  of  the  terreplein, 
it  will  be  only  nccessar}-  to  subtract  8  feet  from  the  cor- 
i-esponding  one  of  the  interior  crests.  Thus,  (8r).50)  being 
a  reference  of  a  horizontal  of  the  interior  crest,  that  of  the 
terreplein  corresponding  is  (77.50.) 

The  terreplein  of  the  curtain  slopes  1  foot  from  the  foot 
of  the  banquette-slope  to  its  inward  line,  which  places  this 
last  line  9  feet  below  the  interior  crest. 

297... Rampart-slope  and  Ramps.  PI.  2,  Fig.  6.  The 
rampart-slopes  are  planes  of  f,  passed  through  the  inward 
lines  of  the  terrepleins.  The  lines  of  intersection  of  the 
rampart-slopes  and  plane  of  site  are  found  in  the  usual 
way. 

The  ramps  leading  from  the  plane  of  site  to  the  terre- 
plein receive  an  inclination  of  ^,  and  they  are  4.30  yards 
wide.  Two  of  them  are  placed  on  the  curtain,  one  on  the 
flank,  and  one  on  the  face. 

298... Analysis  of  Constructions  adopted  for  the  En- 
ceinte. Noizet,  in  the  plan  of  his  euceinte,  has  adopted 
dimensions  and  constructions  which  give  results,  for  the 
most  part,  the  same  as  those  of  Viiuban  and  Cormontaingne, 
making  the  defensive  properties  of  these  diilercnt  methods 
about  equal.  The  extent  of  the  exterior  side,  theMength 
of  the  curtain,  the  diminished  angle,  and  the  direction 
assumed  for  the  flanks,  produce  a  combination  by  which  an 


noizet's  method,  109 

efficient  flanking,  both  as  to  direction  and  anion nt  of  fire, 
for  the  entire  scai-p,  and  a  powerful  cross-tire  upon  tlie  cov- 
ered-waj  and  its  glacis  in  advance  of  the  bastion  salient. 
The  lines  of  defence,  by  this  combination,  being  within  the 
effective  range  of  small  arms,  and  the  flanks  capable  of 
receiving  a  battery  superior  to  the  counter-battery  that  can 
be  brought  against  them  from  the  glacis  crest  of  the  oppo- 
site covered-way. 

299. ..The  dimensions  and  form  of  the  profile  are  those 
usually  adopted  for  permanent  works,  where  the  embank- 
ments are  formed  of  ordinar}"  earth,  and  the  revetement 
walls  of  good  masonry. 

They  are  such  as  experience  has  shown  will  give  dura- 
bility and  stabilit}'  to  the  masonry,  from  the  [)ressure  of  the 
embankments  and  the  ordinary  causes  of  destructibility  to 
which  it  is  liable  when  exposed  to  the  weather ;  and  to  the 
rampart  and  parapet  the  strength  to  resist  the  action  of  the  , 
heaviest  artillery  ;  whilst  they  offer  to  the  assailed  every 
convenience  for  their  prompt  action  and  the  use  of  their 
arms. 

300... The  width  and  slopes  of  the  ramps  are  regulated 
for  the  passage  of  artillery.  Where  the  height  to  be  over- 
come is  slight,  as  that  between  the  terreplein  and  barbette, 
the  slope  of  the  ramp  may  be  as  great  as  ^,  and  its  width 
be  3.30  yards.  Where  the  height  is  greater,  the  declivity 
of  the  ramp  should  be  proportioiuilly  less  steep,  and  its 
width  be  4.30  yards  at  least. 

301. ..The  position  of  the  terreplein  with  respect  to  the 
interior  crests,  is  that  usually  considered  necessary  to  give 
shelter  to  the  troops  and  materiel  on  it.  By  inclining  that 
of  the  bastion,  the  materiel  and  personnel  on  the  faces  and 
flanks  arc  better  covered  from  the  enfilading  and  richochet 
fire  than  they  would  be  if  the  terre[>]ein  was  horizontal: 
as  a  ball  passing  over  the  salient  will  reach  an  inclined 
terreplein  at  a  point  farther  from  the  salient  than  one  which 
is  horizontal.  The  height,  4.50  feet,  at  which  the  salient 
is  placed  above  the  curtain,  is  as  great  as  can  be  admitted 
in  a  hexagon,  the  least  polygon  to  which  the  tra96  adopted 


lie  noizet's  method. 

is  applicable ;  l)ccansc,  if  placed  liiglier,  the  ])lane  of  tlie 
interior  crest  of  the  hastion,  prolonged  hack,  would  inter- 
sect the  ]>lane  of  site  in  a  line  which  would  fall  without  the 
salients  of  the  two  adjacent  hastions  of  the  polygon,  and 
these  hastions  would,  therefore,  not  cover  the  one  hetween 
them  from  reverse  tire. 

The  slopes,  moreover,  of  the  terrepleins  keep  them  in  a 
scrviceahle  state,  by  not  allowing  the  rain-water  to  collect 
and  remain  upon  them. 

302... Particular  Conditions  of  the  Outworks.  The 
outworks,  besides  satisfying  the  general  conditions  already 
laid  down,  are  connected  with  each  other  by  sevefal  minor 
relations  of  defence  and  suitableness,  growing  out  c-f  their 
relative  positions,  which  give  rise  to  manv  seeminglv  arbi- 
trar\'  constructions  and  details  for  each  one,  the  bearing  of 
which  cannot  be  clearly  explained  until  a  description  of  the 
whole  as  a  system  has  been  gone  into. 

803. ..The  scarp  walls  of  outworks,  as  well  as  their  gorges 
where  they  are  exposed  to  be  turned,  should  not  be  less 
than  12  feet  high,  to  secure  them  from  a  sudden  open 
assault. 

304. ..Their  parapets  arc  of  the  same  form  as  that  of  the 
enceinte;  and  for  the  more  important  ones,  which  are  much 
exposed  to  the  artillery  of  the  assailant,  of  the  same  dimen- 
sions. In  those  less  exposed,  the  thickness  of  the  parapet 
may  be  reduced  to  12  feet,  or  4  yards. 

305... The  terrei)leins  of  the  smaller  outworks,  wliich  are 
not  habitually  armed  with  artillery,  should  not  be  less  than 
8  3'ards  ;  those  of  the  larger  should  not  be  less  than  10 
yards. 

306. ..The  banquette-treads  of  outworks,  which,  like  the 
ca})onnieres  and  covered-ways,  require  a  palisading  for 
tlieir  greater  security  from  assault,  should  be  0  feet  wide. 

307...TENAILLE.  PI.  3,  Figs.  1,  2.  The  form  of  the 
tenaille  is  that  of  Cormontaingne's  front;  the  magistral  of 
its  curtain  being  parallel  to  that  of  the  curtain  of  the  en- 
ceinte, and  the  scarp  of  its  wings  on  the  prolongation  of  the 
scarp  of  the  bastion  faces. 


noizet's   method.  Ill 

S08...A  ditch  of  13  yards  is  left  between  the  g()i'2:c  of  tlic 
teiiaille  and  the  enceinte  curtain,  and  one  of  11  yards  be- 
tween each  of  its  wings  and  the  flanks.  The  magistral  of 
its  cnrtain  is  horizontal,  and  13  feet  above  the  crests  of  the 
double  caponnicrc.  The  magistral  of  each  wing  is  a  broken 
line,  the  lowest  point  of  it  being  13  feet  above  the  bottom 
of  the  enceinte  ditch.  Its  gorge  and  the  extremities  of  its 
wings  arc  revetted.  Its  intcrioi-  crest  is  horizontal  thi'ough- 
out,  and  4.")0  feet  below  the  magistral  of  the  enceinte  cur- 
tain. The  thickness  of  its  ]>arapet,  12  feet.  The  width  of 
tlic  terreplein  at  its  curtain,  8.(5(3  yards.  The  para[)et  is 
tci'ininatcd  at  the  wings  by  traverses  12  feet  thick,  which 
extend  from  the  interior  crest  to  the  scarp  wall  of  the 
wings  ;  the  top  of  each  traverse  is  on  the  same  level  as 
the  interior  crest.  The  traverses  are  terminated  toward 
the  parapet  b}'  planes  of  ]. 

309. ..To  construct  the  principal  lines  of  the  tenaille  from 
the  preceding  data,  flrst  draw  a  line  parallel  to  the  enceinte 
curtain,  and  13  yards  from  it,  for  the  gorge  of  the  tenaille 
curtain  ;  another  line  parallel  to  this,  and  at  8.6G  yards,  is 
the  interior  crest,  of  Avhich  the  reference  is  (63.50),  as  it  is 
4.50  feet  below  the  enceinte  magistral  at  the  curtain. 

310...  A  level  passage  at  31.50  feet  below  the  magistral  of 
the  enceinte  curtain  and  at  the  reference  (36.50),  leads  from 
the  main  ditch,  between  the  enceinte  and  tenaille,  under 
this  last  work,  and  through  a  double  caponniere  in  the 
main  ditch  in  advance  of  it.  The  crests  of  the  caponniere 
are  0  feet  above  the  level  of  the  passage  and  at  the  refer- 
ence (45.50);  and  the  magistral  of  the  tenaille  curtain  13 
feet  above  these  crests,  and  at  the  reference  (58.50).  The 
interior  crest  of  the  tenaille  having  the  reference  (63.50), 
is,  therefore,  5  feet  above  its  magistral.  The  horizontal 
distance,  then,  between  the  magistral  and  interior  crest, 
Art.  65,  is  12H  3  1  1.5  16.5  ft.,  or  5.50  yds.;  and  as  these 
lines  are  horizontal,  their  projections  will  be  parallel  and  at 
this  distance  apart. 

311. ..The  interior  crest  and  magistral  of  the  wing  will 
result  from  the  following  data:   The  scarp  wall  of  the  wing 


112  noizet's  method. 

extends  to  the  top  of  the  triiverso  refereiieo  (08.50) ;  its 
maj^istral  then  descends  from  this  level  in  the  plane  of  j, 
wliich  terminates  this  traverse,  to  a  level  of  13  feet  above 
the  bottom  of  the  enceinte  ditch,  which,  being  at  this  i)art 
3  feet  lower  than  the  passage  of  the  double  caponnicre, 
and  at  reference  (33.50),  will  give  (46.50)  for  the  reference 
of  the  lowest  point  of  the  magistral  of  the  wing;  the  rei^er- 
ence  of  the  point  where  it  joins  that  of  the  curtain  being, 
as  already  determined  (58.50). 

312... To  find,  then,  the  lowest  point  of  this  magistral, 
draw  a  line  12  feet,  or  4  yards,  from  the  extremity  of  the 
wing,  for  the  exterior  line  of  the  traverse  ;  parallel  to  this 
line  draw  another  at  17  ft.  =  5.66  yds.,  which  is  the  base  of 
the  slope  of  }  that  terminates  the  traverse,  where  this  line 
cuts  the  line  of  defence  is  the  required  point.  The  hori- 
zontal distance  between  this  point  and  the  interior  crest, 
calculated  in  the  usual  manner,  is  12+15+1.50=28.50  ft.=^ 
9.50  yds. 

313. ..Describing,  from  the  point  just  found,  an  arc,  with 
a  radius  9.50  yards,  and  from  the  other  extremity  of  the 
maffii^tral  another  arc,  with  a  radius  5.50  vards,  and  draw- 
ing  a  tangent  to  these  arcs,  it  will  be  the  interior  crest  of 
the  wings. 

314. ..The  gorge  line  of  the  wing  is  not  drawn  i)arallel  to 
the  interior  crest,  but  determined  as  follows :  From  the 
point  of  intersection  of  the  interior  crests  of  the  curtain 
and  wings,  describe  an  arc  with  a  radius  8.66  yards ;  from 
the  point  where  the  enceinte  curtain  magistral  prolonged 
cuts  tlie  interior  crest  of  the  opposite  flank,  draw  a  line  tan- 
gent to  this  arc,  Avhich  will  be  the  direction  of  the  re(piired 
line. 

31 5... The  gorge  wall  rises  to  the  level  of  the  terreplein. 
That  which  terminates  the  wing  is  limited  by  the  [)lanes 
of  the  parapet,  terreplein,  and  top  of  the  traverse,  and  is 
termed  a  profile  wall,  from  the  form  of  its  outline. 

316... Analysis  of  Constructions,  etc.,  of  the  Tenaille. 
The  tenaille  is  more  important  as  a  mask  than  as  a  defen- 
sive work.     It  covers  the  postern  in  the  curtain,  and  also 


noizet's  method.  113 

the  masonry  of  the  flanks  and  curtain  from  the  enemy's 
batteries;  wliich  last  is  an  essential  point,  if  there  are  inte- 
rior retrenchments  resting  either  on  the  flanks  or  curtain 
of  the  enceinte,  as  it  "vvill  then  be  impracticable  i'or  an 
enemy  to  turn  them,  as  he  cannot  make  a  breach  in  the 
enceinte  behind  the  tenaille.  As  a  defensive  work  its  fire 
bears  upon  the  ditches  and  their  counterscarps,  and  it  thus 
serves  to  cover  the  retreat  of  the  troops  from  the  other  out- 
works. When  the  ditches  are  dry  it  is  an  indispensable 
part  of  the  front,  as  the  space  in  its  rear  forms  a  large  place 
of  arms,  where  troops  can  be  assembled  to  manceuvre 
against  the  euemv  when  in  the  ditches. 

317...A^auban  and  Cormontaingne,  we  have  seen,  so  fixed 
the  relief  of  the  tenaille  as  not  to  mask  the  fire  of  the 
flanks  on  the  breach  in  the  bastion.  It  is  on  this  principle 
that  Noizet  has  determined  the  position  of  its  interior  crest, 
and  placed  it  at  4.50  feet  below  the  magistral  of  the  curtain. 

318... In  regulating  its  scarp  wall,  it  is  supposed  tliat  an 
enemy  would  attempt  an  assault  from  some  point  in  the 
dead  space  in  front  of  it;  and  its  height  is,  thereibre,  ar- 
ranged so  that  no  part  of  it  shall  be  less  than  13  feet  above 
any  point  that  the  enemy  might  there  occupy. 

319. ..The  position  given  to  its  interior  crest  still  leaves 
some  portion  of  the  nuisonry  behind  it  cx[)osed ;  l)ut,  were 
the  exposed  part  battered  awaj-,  there  would  be  still  a  for- 
midable height  of  scarp  left  to  the  enceinte,  the  parapet  of 
wliich,  also,  would  be  but  slightly  diminished  in  thickness 
l)y  it.  The  portion  of  the  enceinte  flank  exposed,  near  the 
shoulder  angle,  would  be  very  con.siderable  were  the  exte- 
rior slope  of  the  tenaille  parapet  extended  to  the  extremity 
of  the  wing;  it  is  to  prevent  this  that  a  traverse  is  liere 
l>lacc'd. 

320... The  tenaille  is  seldom  armed  with  cannon,  although 
mortars  are  frequently  [»laccd  in  it;  on  this  account  i/.s  tcr- 
rcplchi  is  rc'(/t(cc(/  to  8.()()  i/ards. 

321...Kvcry  part  of  the  ditih  between  the  tenaille  and 
curtain  should  be  swept  by  tlie  flanks.     It  is  to  satisfy  thi.s 
condition   that  the  gorge  line  of  the  wing  is  so  drawn  as- 
8 


114  noizet's  method. 

to  be  scH'ii  l)y  tlie  piece  that  flanks  the  c-urtain  of  (lie  on- 
ceinto. 

322. ..The  tonaillc,  altlioiigli  jn'ofuriiii^  (U'cided  advaii- 
ta<j^es  to  the  bastioned  fonii,  deju'ives  it  of  one  of  its  char- 
acteristic points — that  of  Hankint::  every  jtart  of  the  ditch. 
For,  in  front  of  the  tenaille,  there  is  a  dead  space,  where  an 
assailant  could  assemble  in  safety  to  assault  it.  This  defect, 
however,  is  of  ti'ifling  niai^nitude,  since,  were  the  tenaille 
taken,  he  could  not  establish  himself  in  it;  and'the  width 
given  to  the  ditch,  between  it  and  the  enceinte  flank,  is 
such  as  to  preclude  any  attempt  to  escalade  the  enceinte 
from  the  top  of  the  tenaille. 

328. ..The  terreplein  of  the  tenaille  is  inclined,  lor  the 
purpose  of  defiling  it  from  the  enemy's  establishment  on 
the  tcrrcjilein  of  the  demilune  redoubts  The  inclination  of 
the  plane  of  defilement  depends  on  the  arrangement  of  this 
redoubt. 

324. ..Double  Oaponniere.  Tl.  8,  Figs.  1,  2.  The  passage 
of  the  double  caponnicre  is  3.30  yards  wide  at  the  bottom, 
and  on  the  same  level  as  the  bottom  of  the  ditch  at  the 
middle  of  the  curtain  reference  (36.50).  The  interior  crests 
of  this  work  are  at  9  feet  above  the  bottom  of  the  passage  ; 
they  are  horizontal,  and  their  reference  (45.50).  In  the 
profile  of  the  eaponniere,  the  base  of  the  interior  slope  is 
0.50  yards;  the  banquette  is  2.0  yards  wide;  and  the  base 
of  the  banquctte-slo])c,  3.0  yards;  the  horizontal  distance, 
then,  between  the  iiiterioi"  crest  and  the  foot  of  thi'  l)an- 
quette-slope  is,  5.50  yards,  which,  being  doubled  and  ailded 
to  3.30  yards,  the  width  of  the  passage,  gives  14.30  yards  for 
the  distance  between  the  interior  crests.  The  crests  are 
drawn  parallel  to  the  per}»cndicular  of  the  front,  and  lim- 
ited by  the  curtain  of  the  tenaille  on  one  side  and  a  line 
drawn  [>arallel  to  and  3.30  yards  within  the  exterior  side  on 
the  other. 

325. ..The  embankment  of  the  caponnicre  is  terminated 
on  the  exterior  by  a  glacis,  wdiich  is  prolonged  to  tlie  bot- 
tom of  the  ditch.  This  glacis  is  determined  by  jtassing  a 
plane   tliruugh   the   interior  crest  of  the   caixmnicre,   and 


noizet's  method.  115 

througli  tlie  shoulder  angle  of  the  interior  crest  of  the 
()]>}K),site  l)astion  lowered  three  feet. 

o26...The  caponniere  is  terminated  toward  the  exterior 
side  h\  A  profile  wall  along  (he  line,  at  8.30  yards  within 
the  exterior  side ;  this  wall  is  })rolonged  from  the  exterior 
line  of  the  banqnette-trcad  to  a  })oint  at  2.0  yards  beyond 
the  interior  crest;  at  this  }ioint  the  direction  of  the  wall  is 
changed,  so  that,  being  prolonged,  it  may  cut  the  interior 
crest  of  the  enceinte  Hank,  at  a  point  4.0  yards  from  the 
shoulder  angle.  The  remaining  part  of  the  embankment 
on  this  side  is  terminated  in  a  glacis,  the  plane  of  which  is 
passed  through  the  interior  crest  of  the  enceinte  curtain, 
and  through  a  line  on  the  bottom  of  the  main  ditch,  at  4.0 
yards  within  the  exterior  side.  This  plane  intei'scu-ts  the 
first  glacis  in  a  line,  a  b,  PI.  3,  Fig.  2,  which  is  i)rolonged 
to  its  intersection,  b,  with  a  line,  be,  on  the  first  glacis,  at 
6.()6  yards  from  the  interior  crest.  A  part  of  the  first  glacis 
is  termiiuited  at  this  line,  by  a  i)lane  of  }  ;  the  line  of  inter- 
section of  this  }ilane  of  J  with  the  second  glacis,  is  pro- 
longed to  intersect  the  line  of  the  wall  directed  on  the 
flaidv,  which  gives  the  [)oint  where  this  wall  terminates. 

As  the  bottom  of  the  enceinte  ditch  has  not  yet  been 
fixed  throughout,  its  intersection  with  the  first  glacis  still 
remains  to  be  determined. 

327... Analysis  of  the  Double  Caponniere.  The  capon- 
niere serves  both  as  a  communication  and  as  a  defensive 
Work  for  the  ditch.  As  the  former,  the  passage  should 
admit  of  a  convenient  cii'culation,  without  l.ieing  too  wide, 
which  has  determined  its  width  at  3.30  yards.  The  interior 
ci'csts  should  cover  the  troops  within  the  caponniiire  from 
the  enemy's  establishments  on  the  crest  of  the  bastion  cov- 
ered-way;  a  relief  of  'J  feet  lias  been  found  sufficient  for 
this  purpose. 

328. ..As  a  defensive  work,  its  fire  should  sweep  the  ditch. 
It  is  for  this  purpose  that  its  emliankments  are  arranged  on 
the  interior  as  an  ordinary  parapet  and  on  the  exterior  in 
the  Ibrm  of  a  glacis.  Its  baiujuette-tread  is  made  2.0  yards 
wide,  as  it  should  be  jialisaded. 


116  noizet's  method. 

320... In  order  that  the  embankment  of  tlic  capon niere 
may  not,  by  its  relief,  form  dead  spaces  in  the  ditch,  the 
plane  of  the  first  glacis  is  arranged  so  as  to  be  swept  by  the 
artillery  fire  of  the  opposite  flank.  The  plane  of  the  second 
glacis  and  the  return  wall  are  so  arranged  as  to  be  swept 
by  the  fire  of  the  curtain  and  of  a  part  of  the  flank. 

The  portion  of  the  first  glacis,  near  the  extremity,  is  made 
into  a  glacis  couj)^,  leaving  a  suflicient  thickness  of  parapet 
to  cover  the  passage. 

330... Magistrals  of  Demilune  Scarp  and  Counterscarp. 
PI.  3,  Fig.  3.  To  construct  the  magistral  of  the  demilune, 
two  points  are  taken  on  the  exterior  side  at  103  yards  from 
the  perpendicular;  through  these  points  perpendiculars  are 
drawn  to  the  exterior  side  ;  the  points  where  they  cut  the 
magistral  of  the  bastion  fixccs  are  joined,  and  on  this  line 
an  e([ui lateral  triangle  is  constructed,  its  sides  will  give  the 
directions  of  the  magistral  of  the  demilune.  The  extremity, 
b,  of  the  demilune  face,  is  found  by  drawing  a  line  at  11 
yards  without  the  exterior  side. 

The  counterscarp)  of  the  demilune  is  parallel  to  the  scarp 
and  at  18  yards. 

331. ...Counterscarp  of  the  Enceinte.  PI.  3,  Fig.  3. 
To  construct  the  counterscarp  of  the  enceinte,  an  arc  is 
described  from  the  salient  of  the  bastion,  with  a  radius  of 
26  yards;  a  perpendicular,  b  f,  of  6.60  yards,  is  drawn  to  the 
demilune  face;  if  a  tangent  be  now  drawn  to  the  arc,  and 
a  perpendicular  be  demitted  from  the  point  /,  on  the  tan- 
gent, their  point  of  intersection,  /',  should  fall  on  the  line 
drawn  through  the  extremity  of  the  double  caponni^re, 
parallel  to  the  exterior  side.  The  point,  f,  is  found  by  con- 
structing the  curve,  which  is  the  locus  of  the  above  condi- 
tions. The  arc,  with  the  tangent  drawn  through  /',  is  the 
magistral  of  the  counterscarp. 

332... Redoubt  of  the  Re-entering  Place  of  Arms.  PI. 
3,  Fig.  3.  To  determine  the  magistral  of  the  redoubt  of 
the  re-entering  place  of  arms,  a  line  is  drawn  through  the 
point,  b,  of  the  demilune  face,  and  the  extremity  of  the 
curtain,  and  prolonged  beyond  the  demilune  counterscarp. 


noizet's  method.  117 

A  point,  (/,  is  next  taken  on  the  perpendicular,  at  5.0  yards 
from  the  demilune  salient;  and  tliroiigli  this  })oint  and  a 
point,  c,  assumed  on  the  demilune  counterscarp,  an  indefi- 
nite line  is  drawn.  A  line,  c  d,  is  next  drawn,  making  an 
angle  of  60°  with  the  line  a c  Two  lines,  c'  (/'  and  c'  r", 
are  drawn,  the  iirst  parallel  to  cd,  and  4.30  yards  from  it; 
the  second  parallel  to  a  c,  and  at  2.0  yards  from  it.  If 
the  point  of  intersection,  c',  of  these  two  lines  falls  on  the 
line  drawn  through  b,  it  will  he  the  angular  point  of  the 
redoubt;  and  the  line  c'  d',  the  magistral  of  one  of  its  faces. 
If  the  point  e',  does  not  fall  on  the  line  drawn  througli  b, 
then  a  second  point,  c',  must  be  chosen,  and  the  same  con- 
struction be  again  made.  The  different  intersections,  c', 
will  be  points  of  a  curve,  wliieh  is  the  locus  of  the  above 
conditions;  and  the  intersection  of  this  curve  with  the  line 
drawn  through  b,  will  give  the  required  point.  Having  the 
face  c'  <l',  the  other  face  is  determined  as  follows  :  a  line  is 
drawn  parallel  to  the  demilune  counterscarp,  and  at  27.0 
yards  from  it;  a  point  is  found  on  this  line,  at  7.83  yards 
from  c'  d';  from  this  point,  with  a  radius  of  7.83  yards,  an 
arc  is  described;  a  tangent  drawn  to  this  arc,  from  a  point 
on  the  interior  crest  of  the  bastion  face,  at  13  yards  from 
the  pancoupe,  is  the  direction  of  the  required  face,  d'  d"^ 
which  is  terminated  at  the  bastion  counterscarp. 

333. ..PI.  3,  Fig.  3,  and  PI.  4,  Fig.  1.  The  ditch  of  the 
redoubt  is  liorizontal  ;  and  the  reference  of  its  bottom  is 
determined  l)y  supposing  the  jtlane  of  the  superior  slope 
of  the  bastion  face  to  be  prolonged  to  the  enceinte  counter- 
scarp, finding  the  refereiice  of  the  point,  d",  in  this  plane, 
and  taking  a  point  4.50  feet  below  this  ;  the  reference  thus 
found  is  (57.00).  The  scarp  wall  of  the  redoubt  is  13  feet 
high,  the  reference  of  its  magistral  wnll,  therefore,  be 
(70.90). 

334. ..The  salient  of  the  interior  crest  is  5.33  feet  above 
the  nuigistral — its  reference  is,  therefore,  (76.23);  and  its 
projection  is  evidently  the  point  which  we  have  already  de- 
termined, at  7.83  yards  from  the  magistral.  The  inteiii)r 
crest  of  tlie  face,  d'  d'\  litis  a  slope  of  two  feet  from  the 


118  noizet's  method. 

salient  to  the  extremity  of  tliis  face,  which  condition  fixes 
the  extreme  point  of  the  interior  crest  at  7.10  yards  from 
the  magistrah 

TTaving  the  interior  crest  of  one  face,  that  of  the  other, 
c'  d\  is  fonnd  from  the  scale  of  declivity  of  the  plane  of  the 
interior  crest.  This  scale  is  drawn  jiarallol  to  the  hastion 
capital,  and  since  we  have  already  fonnd  two  points  of  the 
interior  crest,  by  referring  them  to  this  scale  we  can,  as  in 
the  case  of  the  bastion,  Art.  204,  determine  any  required 
point  of  the  other  face. 

385.. .A  small  flank  of  6.0  yards  is  made  perpendicular  to 
the  line  c' c",  the  line  of  the  profile  wall  of  the  tace,  c'  d'. 

336. ..The  terreplein  of  the  redoubt  is  8.66  yards  wide ; 
its  gorge  is  revetted  with  a  wall  13  feet  high. 

337... Analysis  of  the  Kedoubt,  etc.  Having  given  the 
construction  of  the  principal  lines  of  the  redoubt,  we  will 
noAv  give  the  reasons  in  support  of  them. 

338. ..We  first  observe  that,  on  account  of  the  ditch  be- 
tween the  tenaille  and  the  enceinte  flank,  a  breach  might 
be  opened  in  the  curtain,  by  means  of  a  battery  estab- 
lished on  the  glacis  of  the  re-entering  place  of  arms,  if 
there  was  no  mask  between  the  ditch  referred  to  and  this 
glacis.  By  placing  the  angle,  c,  of  the  redoubt  on  the  line 
drawn  through  the  extremity  of  the  curtain,  and  the  extrem- 
ity, 6,  of  the  demilune,  it  is  readily  seen  that  these  two 
works,  so  combined,  cover  the  opening  left  by  the  ditch; 
since  it  will  be  necessary  to  battle  down  either  the  angle  c', 
or  the  angle  6,  to  unmask  the  curtain.  The  means  here 
resorted  to  is  of  frequent  use  in  fortification ;  and  the 
problem  may  be  thus  stated:  a  line  being  given,  ivhi''h  is  par- 
tialbj  covered  by  an  existing  mass  from  fires  in  a  given  direriion, 
to  interpose  another  mass  which,  combined  with  the  first,  shall 
eniireh/  mask  the  given  line. 

AVe  have  thus  established  that  the  point,  c',  shall  be 
found  on  the  line  drawn  through  b  and  the  extremity  of 
the  enceinte  curtain. 

The  communication  along  the  gorge  of  the  redoubt  to 
its  ditch,  is  by  means  of  stairs   placed   along  the    profile 


noizet's  method.  119 

wall,  c'c".  The  width  of  the  stairs  is  2.0  yjirds.  The  stairs, 
like  all  other  coniniunicatioiis,  to  be  safe,  must  be  covered 
from  the  enemy's  fire.  The  point  where  the  enemy  can 
establish  himself,  to  fire  on  the  stairs,  is  along  the  crest  of 
the  demilune  covered-way,  around  the  salient  place  of 
arms.  It  is  readily  seen,  from  the  position  of  the  stairs 
and  the  demilune,  that  this  work  will  partiall}'  cover  the 
stairs ;  and,  therefore,  we  shall  only  have  to  interpose  some 
other  mask,  combined  with  it,  to  attain  the  object  in  view. 
The  mask  used  is  the  point  (%  which  is  the  ano-jo  of  mason- 
ry formed  l)y  the  counterscarp  walls  of  the  demilune  and 
redoubt;  the  ditch  of  the  redoubt  beins;  here  4.30  yards 
wide.  The  position  of  the  point  (t^  through  which  the  line 
ac  is  drawn,  is  so  taken  on  the  exterior  slope  of  the  demi- 
lune parapet,  that  the  line  of  fire  drawn  through  it  will 
pass  over  a  man's  head  at  the  top  of  the  stairs. 

339... The  angle,  e',  between  the  profile  w^all  and  face  wall, 
is  made  60°,  as  this  is  the  minimum  angle  for  masonry,  to 
give  it  sufficient  strength.  The  minimum  is  here  taken  to 
bring  the  face,  c'  d',  as  far  in  as  possible,  and  thereby  make 
the  re-entering  as  deep  as  the  case  will  admit  of. 

340. ..The  object  of  the  redoubt  is  to  strengthen  the  cov- 
ered-way, and  sweep  with  its  fire  the  enemy's  establish- 
ments on  the  glacis  of  the  demilune.  The  principal  woi-ks 
on  this  glacis  are  the  breach  and  counter-batteries,  which 
occupy  a  space  of  about  17.0  yards,  estimated  from  the 
crest  of  the  glacis;  if  to  this  we  add  10  yards,  for  the  mean 
width  of  the  covered-way,  we  obtain  the  distance  27.0 
yards,  which  is  the  least  distance  that  the  salient  of  the 
redoubt  can  be  from  the  counterscarj)  of  the  demilune,  to 
sweep  the  entire  flank  of  the  batteries. 

341. ..The  direction  given  to  the  face,  <J'  <l'\  is  such  as  to 
allow  of  its  being  flanked  by  the  bastion  face.  The  face  is 
thrown  out  as  far  toward  the  salient  of  the  bastion  cov- 
ered-way as  possible,  for  the  purpose  of  crowding  the  space 
along  the  crest  of  this  covered-way,  which  tlie  enemy  re- 
quires for  his  batteries. 

342. ..The  redoubt  l>eini;  directlv  in  front  of  the  ba.stion 


1-0  noizet's  method. 

face,  its  relief  should  be  so  reduced  that  the  fire  of  this 
face  inuy  not  he  too  iinu-li  masked.  To  eft'eet  this,  we 
conmioiice  hy  estahlishiiig  the  bottom  of  its  ditch,  so  that 
the  i)oint  of  it  nearest  the  bastion  maj  just  be  seen  by  the 
musketry  fire  of  the  face  ;  we  then  adopt  nearly-  a  mini- 
mum relief  of  scarp  wall ;  finally,  we  arrange  the  interior 
crest  of  one  fiice,  so  as  to  allow  no  exterior  slope  at  one 
extremity,  and  make  the  other  at  the  salient  2  feet  higher. 
This  slope  of  2  feet  and  tlic  direction  given  to  tlie  scale  of 
declivity  of  the  interior  crest,  determine  a  plane  of  defile- 
ment for  the  redoubt,  the  i)rolon<>ati()n  of  which  will  pass 
at  about  3  feet  al)ove  the  salients  of  the  twt)  demilunes, 
which  arc  symmetrically  situated  with  respect  to  the  bas- 
tion capital.  This  is  done  in  accordance  with  a  principle 
generally  adopted,  that  when  one  work  is  less  advanced 
than  another,  and  commanded  by  it,  the  plane  of  its  inte- 
rior crest  prolonged  should  pass  3  feet  above  the  points 
which  the  enemy  can  occupy  on  the  advanced  work — which, 
from  the  nature  of  the  attack,  must  fall  first  into  his  pos- 
session— so  that  he  may  not  have  a  plungiuii::  fire  into  the 
retired  work,  from  his  establishments,  which  arc  generally 
about  3  feet  above  the  parapet  of  the  work  occupied. 

343. ..The  small  flank  of  G.O  yards  perpendicular  to  the 
profile  wall,  is  to  obtain  a  reverse  fire  on  tljc  breach  made 
in  the  deniihme.  The  gorge  of  the  redoubt  is  revetted  to 
secure  it  from  an  assault. 

34-i...]J>E.MiLUNK  KEDOUirr.  PI.  3,  Fig.  3,  and  I'l.  4, 
Figs.  1,  2.  The  salient  of  the  redoubt  is  33.0  yards  from 
the  magistral  of  the  demilune  ;  finding  a  point  on  the  i)er- 
pendicular,  at  this  distance  from  the  magistral,  we  ol)taiu 
the  salient.  The  nuiicistral  of  the  face  is  found,  bv  draw- 
ing  a  line  iVom  this  })oint  to  the  interior  shoulder  angle  of 
the  bastion. 

345. ..To  find  the  position  o\'  the  interior  crests  of  the 
face,  the  reference  of  the  magistral  must  be  given,  and  the 
scale  of  declivity  of  the  plane  of  the  interior  crest.  To 
determine  the  first,  the  salient  of  the  demilune  interior 
crest  is  placed  at  3  feet  below  that  of  the  enceinte  curtain; 


noizet's  method.  121 

this  gives  (78.0)  for  tlic  rcfcrcnt-e  of  this  point.  Tlie  salient 
of  the  magistral  of  the  redoubt  is  tixed  at  8  feet  below  the 
salient  of  the  demilune,  which  gives  its  reference  (70.0). 
The  nuigistral  slopes  from  the  salient  toward  the  exterior 
side,  and  this  slope  is  arranged  so  that  the  point  Avhere  the 
magistral  cuts  the  exterior  side  shall  be  5.70  feet,  or  1.90 
yards  lower  than  the  salient;  the  reference,  then,  of  this 
point  will  be  (04.30).  Having  thus  two  points  of  the 
magistral,  its  position  is  fixed. 

346. ..To  determine  now  the  interior  crest,  a  pancoupe  of 
4.30  yards  is  made  in  the  salient  of  the  redoubt,  and  this 
commands  the  salient  of  the  demilune  by  1.5  feet.  The 
reference,  then,  of  the  pancoupe,  is  (71). 50).  From  the  pan- 
coupe  to  the  gorge  of  the  redoubt,  which  is  on  the  exte- 
rior side,  the  plane  of  the  interior  crest  has  a  slope  of  1.5 
feet,  and  its  scale  of  declivity  is  parallel  to  the  perpendic- 
ular. To  find  the  crest  from  the  above  data,  it  may  be 
observed  that  the  problem  is  similar  to  the  one  already 
solved,  Art.  294,  in  the  case  of  the  bastion  ;  except  here, 
the  magistral  being  an  inclined  line,  the  distance  of  any 
one  of  its  points,  to  the  point  on  the  interior  crest,  con- 
tained in  a  profile,  is  not  known,  since  only  one  of  the 
points  is  given.  The  following  is  the  method,  which 
applies  to  all  similar  cases  for  doing  this:  It  will  be  ob- 
served that,  if  the  foot  of  the  exterior  slope  be  drawn,  it 
will  have  the  same  slope  as  the  magistral.  Through  the 
foot  of  the  exterior  slope,  then,  which  is  known,  the  plane 
of  the  exterior  slope  whose  inclination  is  J,  is  passed.  If 
any  horizontal  line  be  now  drawn  in  this  plane,  the  hori- 
zontal distance,  Art.  294,  between  this  line  and  a  known 
point  of  the  interior  crest,  contained  in  a  profile,  can  be 
readily*  found. 

To  ap[)ly  this  to  the  case  in  point,  first  draw  the  foot  of 
the  exterior  slope,  which  is  0.50  yard  from  the  magistral  ; 
the  reference  of  this  line  at  the  salient  is  (70.0),  and  at  the 
gorge  (64.30).  To  obtain  the  horizontal  of  the  plane  of 
the  exterior  slope  whose  reference  is  (70.0),  describe  from 
the  point  (64.30)  an  arc,  with  a  radius  5.70  feet,  or  1.90 


122  xoizet's  method. 

Yards;  the  taiii^eiit  drawn  to  this  arc  from  the  point  (70.0), 
is  the  required  line.  Tlie  reference  of  the  pancoupe  being 
(79.50),  its  distance  from  tliis  horizontal  line — the  thickness 
of  the  parapet  l)eing  20.0  feet — is  26.17  feet,  or  8.72  yards; 
and  the  reference  of  the  interior  crest  at  the  2:oro:e  beintj 
(78.0),  its  distance  iVoni  the  same  line  is  8.22  yards;  tlie 
two  points  thus  found  fix  the  position  of  the  interior  crest 
of  the  face. 

347... The  redoubt  is  made  with  flanks,  the  interior  crests 
of  which  are  parallel  to  the  perpendicular,  22.0  yards  in 
length.  To  find  the  flanks,  draw  a  line  parallel  to  the 
exterior  side,  and  at  22.0  yards;  where  this  cuts  the  in- 
terior crests  of  the  faces  will  be  the  interior  shoulder 
angles  of  the  redoubt,  from  which  the  flanks  are  drawn 
parallel  to  the  perpendicular. 

The  magistral  of  the  flank  is  horizontal,  its  position  is, 
therefore,  easily  found. 

348. ..Joining  the  point,  i,  of  the  demilune,  with  the 
extremity  of  the  interior  crest  of  the  flank;  the  direction 
of  the  wall  which  terminates  the  flank,  the  ditrli  of  the 
redoubt  and  the  extremity  of  the  demilune  is  found. 

349... The  terrepleiu  of  the  redoubt  along  the  face  is  8.66 
yards  wide;  along  the  flank  the  width  is  11.0  yards.  This 
terrepleiu,  which  is  8  feet  below  the  plane  of  the  interior 
crest,  is  called  the  upper,  to  distinguish  it  from  the  remain- 
ing interior  space,  called  the  lower  terreplein,  and  which  is  13 
feet  below  the  upper.  A  portion  of  the  upper  terreplein, 
for  a  length  of  about  14.0  yards  from  the  extremity  of  the 
flank,  is  sustained  by  a  wall  of  masonr}'.  A  portion  of  the 
interior  space  between  the  terre})leins  of  the  two  flanks,  for 
about  6.0  yards  from  the  exterior  side,  is  excavated  to  the 
bottom  of  the  ditch. 

350... The  upper  terreplein,  along  the  face,  is  connected 
with  the  lower  by  a  slope  of  f.  Two  ramps  3.30  yards 
wide,  with  a  slope  of  ^,  connect  the  two  terrepleins.  The 
details  of  these  constructions  are  best  studied  from  PI.  4, 
Fig.  1.     The  scarp  wall  of  the  redoubt  is  16.50  feet  high. 

351... Analysis,  etc.,  of  the  Demilune  Redoubt.    As  the 


noizet's  method.  123 

object  of  the  demilune  redoubt  has  been  ab-eady  expbiiued, 
the  reasons  for  tlie  constructions  employed  in  determiuing 
its  dimensions,  etc.,  only  remain  to  be  stated. 

352. ..The  redoubt  should  be  as  advanced  as  possible,  to 
see  in  reverse  the  lodgments  of  the  enemy  on  the  glacis  of 
the  collateral  works.  To  effect  this,  its  salient  is  taken  at 
33.0  3'ards  from  the  demilune  magistral;  this  distance  is 
sufficient  to  allow  their  proper  dimensions  to  the  parts  of 
the  demilune. 

353. ..The  face  of  the  redoubt  is  directed  on  the  interior 
shoulder  angle  of  the  bastion,  to  have  its  ditch  flanked  by 
the  bastion  face. 

354... In  itlaeing  the  salient  of  the  magistral  at  8  feet 
l)elow  the  salient  of  the  demilune,  the  top  of  the  scarp  wall 
will  be  nearly  on  the  level  with  the  demilune  terreplein. 
This  arrangement  will  force  an  enemy,  lodged  on  the  demi- 
lune terreplein,  either  to  lower  his  battery,  to  effect  a  breach 
in  the  redoubt,  or  else  to  employ  a  mine  for  this  purpose  ; 
either  of  which  operations  will  cost  him  much  labor  and 
loss  of  time. 

355. ..The  least  command  has  been  given  to  the  redoubt 
over  the  demilune,  to  enable  the  fire  of  the  redoubt  to  sweep 
the  demilune  terreplein.  This  command  of  1.50  feet,  with 
the  slope  given  to  the  plane  of  the  interior  crest,  will 
prevent  an  enemy  from  having  a  plunging  tire  into  the 
redoubt  from  his  lodgments  in  the  demilune. 

356... The  flanks  of  the  redoubt  are  principally  to  procure 
a  reverse  fire  on  the  breach  in  the  bastion  face;  their 
length  estimated  for  3  guns. 

The  piece  nearest  the  extremity  of  one  flank  should  be 
covered  by  the  extremity  of  the  opposite  flank,  from  the 
reverse  tire  which  might  come  through  the  redoubt  from 
the  enemy's  lodgment  on  the  bastion  covered-way. 

The  terrei»lein  (»f  the  flank  is  made  11.0  yards,  as  it  is 
hal»ittially  armed. 

357. ..In  the  outworks,  wherever  it  can  conveniently  be 
done,  bomb-proof  arches  should  be  made,  to  serve  as  maga- 
zines, shelters,  etc.      This  point  has  been  effected  in  the 


124  noizi:t's  method. 

rcHloubt,  hy  the  position  given  to  the  lower  terreplein ; 
by  this  means,  sufficient  space  is  gained  under  the  Ihmk 
for  a  bomb-proof  shelter.  The  terreplein  of  the  flank 
is  sustained  by  a  w:ill,  which  is  the  interior  facing  of  the 
shelter. 

358.  The  scarp  wall  of  the  redoubt  might  have  been 
reduced  to  the  minimum  dimension  of  12  feet.  But,  ou 
account  of  its  importance,  and,  also,  not  to  diminish  too 
much  the  interior  space,  it  has  been  found  that  the  di- 
mensions adopted,  16.50  feet,  best  satisfy  the  rccjuisite 
conditions.  The  top  of  the  wall  slopes  toward  the  gorge, 
so  that  at  the  shoulder  angle  it  may  be  about  4  leet  lower 
than  at  the  salient;  the  object  of  this  is,  to  ex}»ose  as  small 
a  portion  of  the  wall  as  possible  to  the  enemy's  Are  through 
the  demilune  cut,  wliich,  from  its  width,  might  admit  of  a 
breach  being  made  in  the  redoubt,  through  it,  from  the 
enemy's  lodgment  on  the  re-entering  place  of  arms.  It 
will  be  seen  further  on,  how  the  scarp  of  the  redoubt  is 
covered  by  the  bottom  of  the  cut. 

359. ..Demilune  and  its  Cut.  PI.  3,  Fig.  3,  and  V\.  4, 
Fig.  1.  To  return  now  to  the  demilune,  and  flnish  what 
relates  to  it  and  the  cut  in  its  face. 

300... To  construct  the  scarj)  o\'  the  cut,  the  face,  <■'(/',  of 
the  redoubt  of  the  re-entering  }tlace  of  arms,  is  produced  to 
intersect  the  magistral  of  the  demilune;  joining  this  point 
with  the  interior  shoulder  angle  of  the  demilune  redoubt, 
the  magistral  of  the  scar})  is  obtained. 

361... The  exterior  width  of  the  cut  is  found  by  setting  off 
6.60  yards  on  the  demilune  magistral,  from  tlie  point  where 
it  is  intersected  by  the  face,  c'd'.  To  obtain  the  interior 
width,  an  arc,  with  the  radius  of  10  yards,  is  described  from 
the  exterior  shoulder  angle  of  the  demilune  redoubt;  a 
tangent  is  di'awn  to  tliis  arc,  parallel  to  the  face  of  the 
redoubt;  this  tangent  gives  the  direction  of  a  wall  which 
limits  the  cut  on  the  interior,  and  also  the  portion  of  the 
demilune,  from  the  cut  to  the  extremity  of  the  face.  From 
the  point  where  the  nuigistral  of  the  cut  intersects  the  tan- 
gent, set  off  11.0  yards,  which  is  the  width  of  the  cut  on  the 


noizet's  method,  125 

interior.     Tliis  point  joined  with  the  point  on  tlic  exterior, 
gives  the  connterscar[)  of  tlie  cut. 

3G2...A  parapet  20  feet  thick  is  made  behind  the  scarp 
of  the  cut.  The  relief  of  this  parapet  is  so  determined  that, 
at  the  liigliest  point  of  tlie  mas^istral,  which  is  the  point  on 
tlie  interior,  tliere  sliall  1)e  no  exterior  slope ;  wliich  places 
the  interior  crest  3.33  feet  above  the  magistral  at  this  point. 
The  scarp  wall  itself,  at  this  point,  is  13  feet  above  the  bot- 
tom of  the  cut  on  the  interior;  and  the  interior  line  of  the 
bottom  is  13  feet  nearl}'  above  the  bottom  of  the  ditch  of 
the  redoubt.  These  conditions  fix  the  reference  of  this 
point  of  the  magistral  at  (76.17).  The  interior  crest,  which 
is  horizontal,  is,  therefore,  at  the  reference  (79.50). 

363. ..The  bottom  of  the  cut  has  a  slope  of  4.80  feet  from 
the  interior  to  the  demilune  scarp;  and  the  magistral  of  the 
cut  is  parallel  to  the  bottom,  and  at  13  feet  above  it.  This 
gives  the  reference  of  the  exterior  point  of  the  magistral 
(71.37).  The  magistral  of  the  demilune,  from  this  exterior 
point  to  the  point  />,  is  held  horizontal  and  at  the  same 
reference  (71.37).  The  parapet  of  this  jiortion  of  the  demi- 
lune face  is  12  feet  thick;  its  interior  crest  is  determined 
by  passing  a  plane  through  the  interior  crest  of  the  parapet 
behind  the  cut,  and  allowing  the  prolongation  of  this  plane 
to  pass  3  feet  above  the  demilune  salient.  The  preceding 
data  are  sufficient  to  determine  the  lines  in  question. 

364... Analysis  of  the  Cut.  The  cut  isolates  the  part  of 
the  demilune,  near  the  extremity  of  the  face,  from  the 
salient  portion  ;  this  part  being  arranged  with  a  parapet 
behind  the  cut,  can  be  defended  after  tlie  enemy  has  ef- 
fected a  lodgment  on  the  demilune  salient.  The  cut  thus 
prevents  the  enemy  from  driving  the  besieged  from  the 
redoubt  of  the  re-entering  place  of  arms  ;  which  he  might 
do,  were  the  whole  demilune  to  fall  at  once  into  his  pos- 
session. 

365. ..The  position  of  the  cut  is  so  determined  as  to  allow 
the  face  of  the  demilune  redoubt  to  flank  the  face,  c'  d'. 
Widening  the  cut  on  the  interior  facilitates  this  object. 

By  making  the  interior  line  of  the  bottom  of  the  cut  13 


126  noizet's  method. 

feet  above  the  bottom  of  the  ditch,  the  scarp  of  the  demi- 
lune redoubt  is  parti}'  covered ;  and,  at  the  same  time,  an 
obstacle  is  placed  in  the  wa}-  of  an  enemy,  who  might 
attempt  to  carry  the  Avork  behind  the  cut  by  first  getting 
into  the  cut. 

3GG...Tt  will  be  seen,  in  examining  the  demilune  ditch, 
that  the  slope,  4.80  feet,  given  to  the  bottom  of  the  cut,  still 
leaves  a  height  of  15  to  18  feet  between  the  exterior  line 
and  tlic  l)(»tt()ni  of  the  doinihuK'  ditch,  whicli  \\ill  secure 
the  cut  from  an  assault  on  that  side.  The  object  of  this 
slope  is  chiefly  so  to  diminish  the  height  of  that  part  of  the 
demilune  scarp,  from  the  cut  to  the  point  b,  that  it  may  not 
be  exposed  to  a  battery,  which  can  be  placed  on  the  glacis 
of  the  re-entering  place  of  arms. 

367... As  to  the  interior  crest,  it  is  placed  as  low  as  pos- 
sible, and  is  arranged  to  cover  the  interior  from  the  plung- 
ing fire  of  the  enemy  when  established  on  the  demilune 
salient. 

368. ..Demilune.  PI.  4,  Fig.  2.  To  return  to  tlie  demi- 
lune, of  which  only  the  magistral  and  the  relief  of  the  inte- 
rior crest  at  the  salient  have  been  determined. 

The  magistral  at  the  salient  is  i)laced  11.40  feet  below 
the  interior  crest ;  and  as  the  reference  of  the  latter  is 
(78.0),  the  reference  of  the  former  will  be  (66.60).  The 
magistral  has  a  slope  of  1.50  feet  from  the  salient  to  the 
cut ;  and  the  interior  crest  is  parallel  to  the  magistral;  this 
condition  will  determine  the  interior  crest  when  the  salient 
is  known  ;  and  this  is  arranged  so  as  to  have  a  pancoup6 
of  4.30  yards. 

The  scarp  wall  of  the  demilune  is  22.50  feet  high. 

369. ..The  terrei)lein  is  11.0  yards  wide.  A  ramp,  3.30 
yards  wide,  having  a  slope  of  J,  leads  from  the  ditch  of  the 
demilune  redoubt  to  the  demilune  terreplein.  The  posi- 
tion and  arrangement  of  the  ramp  are  shown  in  PI.  4, 
Fig.  2. 

370. ..The  terreplein  is  finished  by  a  slope  of  earth,  in- 
stead of  being  sustained  by  a  wall.  This  slope  is  thus 
arranged:  the  part  terminating  the  ramp  is  a  plane  of  {  ; 


noizet's  method.  127 

the  position  in  the  angle  is  formed  by  an  inclined  c^'lindri- 
cal  surface,  which  touches  the  two  interior  lines  of  the 
terreplcin  ;  the  Avidth  of  the  ditch  at  the  salient  of  the 
redoubt,  terminated  b}-  the  l)ase  of  the  cylinder,  is  4.30 
yards.  The  remaining  portion  of  the  slo})e  is  formed  of  a 
Avarped  sniface,  the  elements  of  which  are  horizontal,  con- 
necting the  cylinder  and  the  plane  of  }.  This  construction 
is  purely  arl)itrar3' ;  the  oiyect  being  to  luive  the  portion  of 
the  slope  in  the  salient  as  gentle  as  practicable,  so  that  this 
part  may  serve  as  a  ramp  for  infantry. 

371... Analysis  of  the  Demilune,  etc.  The  })rinci[tal 
properties  of  the  demilune  were  mentioned  in  describing 
C'ormontaingne's  method  ;  and  it  was  there  observed  that 
he  improved  upon  Vaul)an's,  by  augmenting  the  dimen- 
sions of  the  demilune.  Engineers,  since  Cormontaingne, 
finding  that  the  demilune  still  admitted  of  being  eidarged 
with  advantage,  have  accordingly  so  determined  its  dimen- 
sions, that  it  may  be  thrown  so  far  to  the  front  as  will  still 
place  the  breach,  which  an  enemy  mux  make  in  its  face, 
within  the  range  of  the  musketry  of  the  bastion  face.  In 
large  fronts,  like  this  under  consideration,  the  demilune 
may  be  thus  made  to  cover  about  30  3^ards  of  the  bastion 
faces  from  the  shoulder  angle,  and  thus  secure  retrench- 
ments resting  against  this  part  from  being  turned  by  a 
breach  made  near  the  shoulder  angle. 

372. ..These  considerations  limit  the  salient  angle  of  the 
demilune  to  60°,  and  place  the  salient  at  not  more  than 
2lO  yards  from  the  bastion  face,  as  this  di.stance  will  bring 
the  breach  at  about  180  yards  from  this  face,  or  within  the 
effective  range  of  musketry. 

373. ..The  demilune  tlius  arranged  jdaccs  the  ba.stions,  in 
all  cases,  in  strong  re-en teriii ga ;  but  when  the  angles  of 
the  polygon  are  very  obtuse,  the  faces  of  the  bastion.s,  pro- 
longed, also  foil  within  the  salients  of  the  demilunes,  and 
are,  therefore,  not  easily  enfiladed.  The  fire  from  the  demi- 
lune is  very  eftectivc  on  the  enemy's  works  along  the  bas- 
tion capitals.  Finally,  it  is  a  work  of  wliich  the  enemy  can 
only  obtain  possession  after  great  labor  and  loss  of  time; 


128  noizet's  method. 

and  when  carried,  it  is  with  great  difficulty  that  lie  can  ren- 
der it  tenable,  as  it  is  exposed  to  the  tire  of  the  enceinte, 
within  a  short  range. 

374... The  demilune,  with  these  advantages,  is  not  with- 
out detects.  Its  faces,  from  their  position,  are  ex[)osed  to 
an  entilading  lire ;  it  dej>rives  the  curtain  of  all  action  on 
the  exterior  ground  ;  and  it  is  only  when  the  angles  of  the 
bastion  arc  very  open,  that  the  re-enterings  formed  by  the 
demilunes  become  of  a  formidable  character.  The  glacis 
of  the  demilune  covered-way  forms  a  ridge,  which  is  ser- 
viceable to  the  enemy  by  masking  his  works  on  one  side  of 
tlie  ridge  from  tlie  lire  of  the  collateral  works  on  the  other. 

Having  noticed  these  general  properties  of  the  demilune, 
the  further  jtarticular  constructions  may  be  examined. 

375. ..In  terminating  the  face  at  11.0  yards  from  the  exte- 
rior side,  a  passage  made  along  the  extremity  of  this  face, 
and  a  face  cover  for  the  bastion,  of  which  mention  will  be 
made  farther  on,  are  allowed  tor  ;  moreover,  the  Hank  of 
the  demilune  redoubt,  intended  to  defend  the  breach  in 
the  bastion  lace  by  a  reverse  lire,  is  unmasked  by  it. 

376. ..The  command  of  the  curtain  over  the  demilune  is 
reduced  to  the  minimum  ;  and  to  obtain  as  much  interior 
space  for  the  demilune  redoubt  as  practicable,  the  height  of 
tlie  interior  crest  above  the  magistral  is  lixed  at  11.40  feet, 
the  interior  space  evidently  depending  on  this  height.  The 
terreplein  is  reduced  to  11.0  yards,  partly  for  the  same 
reason,  and  }):ii-tly  to  give  an  oiemy  great  trouble  in  estab- 
lishing a  battery  on  it ;  as,  to  do  this,  he  will  be  obliged  to 
cut  away  a  })art  of  the  parapet,  and  will  thus  expose  the 
rear  of  the  l)attery  to  the  fire  from  collateral  works. 

377... The  terreplein  is  terminated  by  a  slope  of  earth,  for 
economy,  and,  also,  because  this  slope  is  favorable  to  ollen- 
sivc  movements  made  to  drive  the  enem}'^  from  the  breach. 

378. ..It  is  not  probable  that  an  enemy  would  attempt  to 
carry  the  demilune  by  escalade  ;  it  is  well,  however,  to  pro- 
vide against  such  an  attempt  in  so  important  a  work  ;  it  is 
chiefly  on  this  account  that  the  scarp  wall  is  made  22.50 
feet  hiirh.     This  dimension  also  allows  the  bottom  of  the 


noizet's  method.  129 

cnt  to  he  so  placed  tliat  it  can  be  swept  by  tbc  fire  of  tlie 
deniihinc  redoubt. 

879. ..Face-cover  of  the  Bastion.  PI.  8,  Fig.  3,  and  IN. 
4,  Fig.  1.  By  prolonging  the  bastion  counterscarp  to  the 
point/',  it  serves  as  a  face-cover  to  the  bastion  scarp,  mask- 
ing it  from  the  fire  of  the  breach  battery  erected  around 
the  salient  place  of  arms  of  the  demilune  covered-way. 
The  angle,/',  of  the  face-cover  is  placed  on  the  same  line  as 
the  extremity  of  the  double  caponniere,  for  the  i)uri)Ose  of 
covering  the  troops,  as  they  debouch  from  the  caj)onniere, 
from  the  enemy's  estal)lishment  along  the  glacis  of  the  bas- 
tion covei'cd-way.  The  height  of  the  Avail,  at  the  point  /"', 
is  so  determined  as  to  intercept  the  enem3-'s  fire,  coming 
from  a  point  8  feet  above  the  crest  of  the  bastion  covered- 
way,  and  passing  at  7.50  feet  above  the  bottom  of  the  ditch, 
at  the  extremity  of  the  caponniere.  From  the  point  /',  to 
the  gorge  of  the  redoubt  of  the  re-entering  place  of  arms, 
the  top  of  the  wall  ascends,  so  as  to  cover  the  ramp  leading 
from  the  ditch  to  the  top  of  the  counterscarp  at  //',  and 
also  the  passage  leading  from  this  point  to  the  gorge  of  the 
redoubt. 

880. ..Single  Caponniere  and  Traverse  in  the  Demilune 
Ditch.  This  last  passage  is  also  covered  from  the  enemy's 
works  on  the  glacis  of  the  demilune  salient  place  of  arms, 
by  the  crest  of  a  single  caponniere,  in  the  ditch  of  the 
demilune.  The  glacis  of  this  work  is  determined  by  pass- 
ing a  plane  through  the  point,  (88.40),  of  the  interior  crest 
of  the  bastion  face,  found  by  producing  back  the  demilune 
magistral,  and  through  two  other  points  in  the  demilune 
ditch  :  one  taken  at  13  feet  below  the  ditch  of  tlie  redoubt 
of  the  re-entering  place  of  arms;  the  other,  at  about  16. AO 
feet  below  the  cut  in  the  demilune.  The  crest  of  the 
caponniere  is  held  in  this  plane;  and  in  projection,  is  drawn 
l>arallel  to  the  magistral  of  the  face-cover,  so  as  to  allow 
space  enough  between  it  and  the  foot  of  the  wall,  which 
terminates  the  demilune  face,  for  a  banquette-tread  of  2 
yards,  and  its  slope  of  J  ;  all  of  which  will  rerpiire  about 
4.80  yards.  The  passage  referred  to  is  4.30  yards  wide.  In 
9 


130  noizet's  method. 

order  tliat  it  shall  ho  covered  l)v  the  crest  of  the  capon- 
iiiere.  the  hottom  of  it  must  he  at  least  8  feet  helow  tlic 
crest. 

381. ..The  preceding  construction  suhsers'cs  two  purposes: 
1st,  from  the  position  of  the  glacis  it  is  swept  h}-  the  fire 
of  the  l)astion  face  ;  so  that  tlie  dead  space,  wliieh  was 
noticed  at  this  point  of  the  demilune  ditch,  in  OornK^i- 
taingne's  method,  is  here  removed ;  2d,  it  covers  the 
troops  crossing  the  demilune  ditch  from  the  fire  coming 
from  the  demilune  salient  })lacc  of  arms. 

382. ..As  it  is  important  to  keep  this  passage  open,  even 
after  the  enemy  ohtains  possession  of  the  demilune,  a  trav- 
erse is  placed  at  the  extremity  of  the  caponniere,  so  as  to 
cover  the  postern  which  communicates  with  the  terreplein 
of  the  redoubt  of  the  re-entering  place  of  arms.  A  por- 
tion of  this  traverse  has  to  be  sustained  by  a  wall,  which  is 
so  arranged  as  to  aftbrd  the  least  possible  shelter  to  an 
enemy,  who,  from  behind  it,  might  attem})t  to  carry  the 
redoubt  by  the  gorge. 

388. ..The  face-cover  is  terraced,  the  embankment  being 
2. no  yards  thick  at  top,  and  sloped  inward  toward  the 
passage. 

Remark.  The  details  of  this  part  of  the  construction 
])eing  rather  complicated,  will  be  better  understood  by 
referring  to  PI.  4,  Fig.  1,  than  by  any  written  explanation. 

384... Mask  in  the  Demilune  Kedoubt  Ditch.  PI.  4, 
Fig.  1.  To  cover  the  curtain  wall  from  a  fire  through  the 
opening  between  the  flank  and  the  tenaille,  coming  from  a 
battery  estal)lished  on  the  demilune  terreplein,  an  embaidv- 
ment  is  formed  in  the  ditch  of  the  demilune  redoubt,  the 
wall,  which  separates  this  ditch  from  that  of  the  enceinte, 
being  built  high  enough  to  sujijiort  the  embankment.  The 
embankment  is  sloped  on  top,  and  terminates  in  a  point 
near  the  demilune  cut,  being  terminated  on  tlie  side  toward 
the  redoubt  by  a  slope,  the  foot  of  whicli  is  4.30  yards  from 
the  foot  of  the  redoubt  scarp.  The  crest  of  the  embank- 
ment is  on  the  line  drawn  through  the  shoulder  angle  of 
the  redoubt  and  tlie  anijle  of  the  tenaille. 


noizet's  method.  131 

385.,. The  bottom  of  the  ditch  between  the  embankment 
and  redoubt,  is  about  12  feet  above  tliat  of  the  enceinte 
ditch,  which  secures  the  dcniihinc  from  being  turned 
through  tliis  ditch. 

386... By  separating  tlie  embankment  from  the  demilune 
redoubt,  this  work  is  secured  from  aii  attempt  to  carry  it 
from  the  embankment.  For  the  same  reason,  tlie  gorge 
wall  bcliind  the  cut  is  raised  13  feet  above  tlie  toj*  of  the 
embankment.  A  like  ex})cdient  is  resorted  to  in  all  similar 
cases,  as  in  the  gorge  wall  of  the  redoubt  of  the  re-entering 
place  of  arms,  and  the  coiInterscar[i  of  the  demilune  cut,  as 
shown  in  the  details  on  PI.  4,  Fig.  1. 

387...C0VERED-WAY8.  PI.  5,  Figs.  1,  2.  Tlie  bastioned 
covered-wav  is  11.0  yards  wide — the  interior  crest  being 
drawn  parallel  to  the  counterscar[). 

388... The  crests  of  the  re-entering  place  of  arms  are 
drawn  parallel  to  the  magistral  of  the  redoubt,  and  20  vards 
from  it. 

389. ..The  crest  of  the  demilune  covered-way  is  a  broken 
cremaillere,  or  crochet  line.  The  short  branches  of  the 
cremaillcre  are  6.60  yards  long,  and  are  perpendicular  to 
the  direction  of  the  demilune  capital. 

3110... Remarks  ox  the  Traverses  and  the  Defiles.  The 
objects  of  the  short  branches  of  the  crochets  are  to  cover 
the  defiles^  or  passages,  between  the  ends  of  the  traverses 
and  the  crest  of  the  cove  red- way ;  and  to  give  a  column  of 
tire  in  the  direction  of  the  demilune  capital.  To  fulfil  this 
last  object,  the  short  branches  are  provided  with  a  ban- 
quette, with  a  slope  of  only  j,  to  bring  the  crest  of  this 
branch  as  near  as  [iracticable  to  the  traverse.  A  passage  of 
2.0  yards  is  left  between  the  foot  of  the  banquette-slope 
and  the  wall,  whith  terminates  the  end  of  the  traverse:  the 
direction  of  this  wall  is  parallel  both  to  the  long  and  short 
branches  of  the  crotchets,  leaving  a  passage  between  it  and 
the  long  branch,  2.0  yards  wide. 

31*1. ..To  iind  the  po.siti(Ui  of  the  short  branch,  the  base 
of  the  interior  slope  being  \J)  feet,  the  banquette-tread  6 
feet,  the  base   of  the  banquette-slope    3.o0    feet,  and   the 


132  notzet's  method. 

width  of  the  defile  6  feet  — 17  feet,  or  5.f>6  j-ards,  is  the 
entire  distance  sought  between  the  crest  of  the  short 
branch  and  tlie  wall  that  terminates  the  traverse  parallel 
to  this  branch. 

392... The  portion  of  the  long  branch,  opposite  the  trav- 
erse, is  without  a  banquette,  etc.,  for  the  purpose  of  leav- 
ing the  least  distance  between  the  crest  of  the  crotchet  and 
the  traverse,  so  that  tlie  defile  may  be  covered  in  the  best 
manner.  To  effect  this,  a  vertical  wall  is  placed  parallel  to 
the  end  of  the  traverse,  and  at  2.0  yards  from  it,  to  leave 
space  for  the  defile;  this  wall  sustains  the  earth,  but  is  not 
built  up  higher  than  within  1.50  feet  of  the  crest.  The  earth 
of  the  glacis  lias  the  natural  slope  of  j  from  the  crest  to  the 
top  of  the  w^all ;  the  base  of  this  slope,  consequently,  will 
be  1.50  feet,  and  a  berm  of  0.50  feet  being  left  on  the  top 
of  the  wall.  These  distances,  together,  give  2.66  yards  for 
the  distance  between  the  crest  of  the  long  branch  and  the 
wall  parallel  to  it,  which  terminates  the  traverse. 

303... Traverses  on  the  Demilune  Covered-way.  There 
are  four  traverses  on  the  demilune  covered-way ;  which,  to 
avoid  repetitions,  will  be  designated  as  No.  1,  No.  2,  No.  8, 
and  No.  4  —  No.  1  being  nearest  the  re-entering  place  of 
arms. 

394..  To  construct  the  crotchets  of  traverses  Nos.  1  and 
2,  a  line,  Im,  is  drawn  parallel  to,  and  at  13.0  yards  from, 
the  demilune  counterscarp ;  parallel  to  this  line,  and  at  a 
distance  of  6.60  yards,  measured  on  a  perpendicular  to  the 
demilune  capital,  a  second  line,  I'  m',  is  drawn.  The  salient 
and  re-entering  angles  of  the  crotchets,  between  Nos.  1  and 
2,  rest  on  these  two  lines. 

395... To  construct  traverse  No.  1,  a  line,  nn',  is  drawn 
parallel  to  V  m',  and  at  2.66  yards;  from  the  point  of  inter- 
section, n,  of  tliis  line  with  the  crest  of  the  re-entering 
place  of  arms,  a  line,  n  o,  is  drawn,  so  that  its  intersection, 
0,  with  the  demilune  counterscarp,  shall  be  perpendicular 
to  a  line  drawn  from  o,  to  the  point  «,  on  the  demilune. 
The  line  n  o,  is  the  interior  crest  of  No.  1.  The  exterior 
crest,  v'  o',  is  parallel  to  it,  and  at  6.66  yards. 


noizet's  method.  133 

306... From  the  point  u\  as  a  centre,  with  a  radius  of  5.6() 
yards,  an  arc  is  descrihcd  ;  a  tangent  drawn  to  this  arc, 
perpendicuUir  to  the  demilune  caitital,  gives  the  short 
branch   of  the  crotchet. 

397... To  construct  traverse  No.  2:  from  the  extremity  of 
the  short  crotchet,  just  found,  with  a  radius  of  G.GO  yards, 
an  arc  is  described ;  a  tangent,  drawn  fiom  the  point  a  to 
tliis  arc,  will  give,  l)y  its  intersection,  o,  with  the  counter- 
scarp, a  point  of  the  interior  crest  of  No.  2;  the  interior 
crest  is  drawn  from  this  point,  perpendicular  to  the  tan- 
gent. The  exterior  crest,  ?i'  o',  is  drawn  at  4.33  j-ards  from 
n  0. 

3IKS...T0  obtain  the  crotchets  from  anj-  assumed  jjoint,  n', 
of  this  exterior  crest,  with  radii  of  2.6G  and  5.66  yards,  two 
arcs  are  described;  tangents  arc  drawn  to  these  arcs  —  one 
from  the  inner  extremity  of  the  short  branch  of  No.  1  to 
the  arc  of  2.66  yards,  the  other  to  the  arc  of  iJ.Gij  yards, 
and  perpendicular  to  the  demilune  ca})ital.  If  these  two 
tangents  intersect  on  the  line  I'm',  then  the  point  n'  is 
one  point  of  the  end  No.  2,  and  the  line  /i  11/  is  di'uwn  jiar- 
allel  to  the  long  branch  ;  if  the  tangents  do  not  intersect 
on  I'  tii\  then  some  other  point,  ?i',  must  be  chosen,  and  a 
similar  construction  made,  until  the  intersection  is  found 
on  the  line  U  )ii',  which  will  be  the  salient  angle  of  the 
crotchets. 

399... To  construct  No.  3  and  its  crotchets,  a  point  is 
taken  on  the  short  branch  of  the  crotchet  last  found,  at  4.30 
yards  from  its  salient  angle ;  froni  this  point  an  arc  is  de- 
scribed, with  a  radius  of  4.50  yards  ;  a  tangent  drawn  to 
this  arc  from  the  point  ",  will  give  the  point,  0.  on  the 
countcr.-carp,  where  the  interior  crest  of  No.  3  is  to  be 
drawn,  perpendicular  to  the  tangent.  The  exterior  crest  of 
this  traverse  is  at  4.33  yards  from  the  interior  crest. 

400. .The  short  branches  of  the  crotchets  of  No.  3  and 
No.  4,  have  the  same  direction  as  the  others;  but  tliey  are 
limited  by  two  lines,  one  drawn  parallel  to  the  counter- 
scarp, and  at  11.0  yards  from  it,  the  other  at  6.(J0  yards 
from  this,   measured  on  a  perpendicular  to  the  demilune 


134  noizet's  method. 

capital.  Tliese  two  lines  being  drawn,  the  position  of  the 
salient  and  re-entering  angles  of  the  crotchets  that  rest 
upon  thorn  will  be  found  by  a  construction,  similar  to  the 
one  jii.st  described. 

401... The  re-entering  angle  of  the  crotchet  of  No.  2  is 
cut  off,  b}'  drawing  a  line  throngh  the  centre  of  the  are, 
and  parallel  to  the  tangent  drawn  to  it  from  a. 

402... To  construct  No.  4,  commence  by  finding  the  foot 
of  its  exterior  slope.  This  is  done  by  descril)ing  an  arc 
from  the  angular  point,  c',  of  the  redoubt  of  the  re-entering 
place  of  arms,  with  a  radius  of  4.30  yards;  a  tangent  drawn 
to  this  arc,  through  the  demilune  salient,  being  produced 
to  the  covered-way,  gives  the  foot  of  the  exterior  slope. 
The  interior  crest  of  No.  4  is  parallel  to  this  line;  its  posi- 
tion is  found  by  allowing  4.66  feet,  or  1.55  yards,  for  the 
base  of  the  exterior  slope,  and  20  feet,  or  ^.QQ  yards,  for 
the  thickness  of  parapet.  Having  the  exterior  and  interior 
crests,  the  point  n',  and  the  crotchets,  are  found  as  in  the 
preceding  cases. 

403... The  interior  crest  of  the  salient  place  of  arms  is  on 
the  line,  Im^  produced;  which  is  at  11.0  yards  from  the 
counterscarp.  A  pancoupe  of  4.30  yards  is  made  in  the 
salient. 

404... Traverse  on  the  Bastion  Covered-way.  PI.  5, 
Fig.  1.  To  construct  the  traverse  and  its  crotchets  on  the 
bastion  covered-way,  a  line,  tr,  is  drawn  at  5.50  yards,  par- 
allel to  the  crest  of  the  bastion  covered-way;  the  extremity 
of  the  traverse,  nn'^  is  drawn  parallel  to  tr,  and  2.60  yards 
from  it.  From  the  point  w,  on  the  crest  of  the  re-entering 
place  of  arms,  the  interior  crest  of  the  traverse  is  drawn 
per[)endicular  to  the  bastion  counterscarp.  The  exterior 
crest  is  20  feet,  or  6.66  yards,  from  the  interior  crest. 

To  find  the  other  branch  of  the  crotchet,  n  n'  is  taken, 
equal  to  5.0  yards  ;  a  line  is  drawn  through  r  and  n\  and 
produced  to  s,  on  the  crest  of  the  bastion  covered- way  ;  an 
arc,  with  a  radius  of  2.66  yards,  is  now  described  from  n'y 
and  the  tangent,  s  t,  drawn  to  this  arc,  is  the  branch  re- 
quired. 


noizet's  method.  135 

405... Command  of  the  Covered-way  and  Traverses.  PI. 
f>,  Fig.  2.  To  arrange  the  relief  of  the  covered-wa}^  and 
traverses,  the  following  method  is  pursued  :  The  salient  of 
the  demilune  covered-way  is  7.50  feet  lower  than  the 
salient  of  the  demilune;  the  reference  of  this  point  then  is 
(70.50).  The  interior  crests  of  the  salient  place  of  arms  of 
traverse  No.  4,  and  the  long  branch  between  IS^os.  3  and  4, 
are  held  in  the  same  plane  ;  the  scale  of  declivity  of  which 
is  parallel  to  the  demilune  capital ;  its  inclination  being 
determined  by  placing  the  extremity  of  the  long  l)ranch, 
just  referred  to,  0.75  feet  lower  than  the  salient  of  the  demi- 
lune covered-way. 

406... The  short  branch  of  the  crotchet  of  Xo.  8  has  the 
same  reference  as  the  salient  of  the  covered-way,  (70.50). 
This  line,  the  interior  crest  of  No.  3,  and  the  long  branch, 
are  held  in  the  same  plane,  whose  scale  of  declivit}-  is  par- 
allel to  the  demilune  capital,  and  whose  inclination  is  such 
that,  being  produced,  it  will  pass  3  feet  above  the  salient  of 
the  covered-waj-. 

407... The  relief  of  No.  2  and  its  crotchets  is  determined 
in  the  same  manner  as  in  the  preceding  case.  The  refer- 
ence of  the  short  branch  being  fixed  at  (70.20). 

408. ..The  salients  of  the  bastion  covered-way,  and  the 
re-entering  place  of  arms,  command  the  salient  of  the 
demilune  covered-way  by  1.50  feet.  Their  reference,  there- 
fore, is  (72,0). 

409... Remarks  on  the  Covered-ways  and  Traverses. 
The  demilune  covered-way  is  made  wider  toward  the  re- 
entering, to  cover  the  traverse  defiles  with  more  ease. 
The  width,'  11.0  yards,  of  the  portion  near  the  salient, 
makes  the  covered-way  so  narrow  that,  should  an  enemy 
find  it  necessary  to  lower  his  breach  l)attery  into  it  to 
ett'ect  a  [>racticable  breach,  lie  will  be  obliged  to  cut  away 
a  part  of  the  glacis  to  obtain  suflicient  room  for  his  works. 

410. ..The  counterscarp  of  the  redoubt  of  the  re-entering 
l>lace  of  arms  is  a  slope  of  earth,  so  as  to  make  the  re- 
entering place  of  arms  more  spacious,  by  joining  the  ditch 
of  its  tcrreplcin. 


136  NOIZET'S    iMETIIOD. 

411...Tlie  interior  crests  of  the  re-ciitoriiig  place  of  arms 
and  its  two  traverses  are  held  in  tlie  same  plane,  whose 
scale  of  declivity  is  parallel  to  the  bastion  capital.  Tiiis 
plane  prodnced,  passes  3  feet  above  the  salients  of  the  two 
collateral  demilunes,  from  which  this  place  of  arms  is  thus 
defiled. 

412... The  crests  of  the  bastion  covered-way  are  in  the 
same  plane,  whose  scale  of  declivity  is  parallel  to  the  bas- 
tion capital.  This  plane,  prolonged,  also  passes  3  feet  above 
the  same  points  as  the  last  mentioned,  and  for  the  same 
object. 

413... The  traverses  serve  as  masks  to  cover  the  tcrreplein 
of  the  covered-way  from  ricochet  shots;  for  this  purpose, 
Nos.  2  and  3  may  be  only  4.33  yards,  or  13  feet  thick.  But 
the  other  traverses,  which  close  the  re-entering  and  salient 
places  of  arms,  being  more  important,  have  a  thickness  of 
6.66  yards.  As  the  general  height  of  the  traverses  is  2.66 
yards,  it  is  readily  seen  that,  supposing  the  extreme  limit 
of  ricochet  firing  to  ])e  an  angle  of  j\,  the  traverses  should 
not  be  more  than  2(3.6  yards  apart,  in  order  that  a  shot 
striking  the  crest  of  one  may  imbed  itself  in  that  immedi- 
ately in  rear  of  it. 

414... The  traverses  also  serve  as  a  defence;  and  for  this 
purpose  are  made  like  an  ordinary  parapet.  To  enable  the 
besieged  to  defend  the  covered-way,  they  are  palisaded,  and 
barriers  are  placed  at  the  defiles.  As  the  means  of  pro- 
tracting the  defence  are  only  eftective  when  the  defiles  are 
perfectly  secured  from  the  fire  of  the  enemy,  estal)lished 
along  the  crest  of  the  salient  place  of  arms,  the  reason  for 
the  particular  construction  given  for  each  travc^rse  will  now 
be  apparent.  The  interior  crests  of  IsTos.  1,  2  and  3  are 
so  arranged  that  they  can  cf>ncentrate  their  fire  on  the 
salient  place  of  arms;  and  each  traverse  is  so  combined 
with  the  demilune,  as  eftectually  to  mask  the  defile  of  the 
one  in  rear  of  it.  The  defile  of  No.  1  is  masked  by  No.  2, 
ami  a  passage  of  about  2.0  yards  at  the  foot  of  the  ban- 
quette-slope .of  No.  1  is  covered,  so  that  the  troops  can 
pass  through  this  defile  in  perfect  safety. 


noizkt's  method.  137 

415...TliG  defile  No.  2  is  less  casil}-  covered  l)y  No.  3. 
To  eft'ect  it,  the  inner  angle  of  the  crotchets  has  to  be  cut 
oft"  and  the  hanqiiette-vslope  suppressed,  snbstitntino-  in  its 
place  steps;  by  these  means,  a  passage  of  1.0  yard  is  cov- 
ered, and  No.  3  placed  not  too  far  from  No.  2. 

410... As  it  is  not  })racticable  to  cover  the  defile  of  No.  3, 
the  position  of  No.  4  is  determined,  so  as  to  make  the 
salient  place  of  arms  as  spacious  as  possible.  This  is  done 
by  placing  No.  4  in  a  position,  to  allow  its  exterior  slope  to 
be  swei>t  l)y  the  fire  of  the  bastion  face,  penetrating  be- 
tween the  salient  of  the  demilune  and  the  angle  of  the 
redoubt  of  the  re-entering  place  of  arms. 

41 7... The  defile  of  the  traverse  on  the  bastion  covered- 
way,  is  arranged  to  prevent  any  line  of  fire  penetrating 
through  it  into  the  re-entering  place  of  arms. 

418. ..The  precautions  which  are  here  taken  wonld  be 
still  insufficient,  could  the  enemy,  in  possession  of  the  crest 
of  the  salient  place  of  arms,  have  a  plunging  fire  upon  the 
covered-way  behind  the  traverses.  It  is  to  prevent  this 
that  the  interior  crests  of  the  different  traverses  and  their 
respective  crotchets  are  held  in  the  same  plane;  which  is 
so  arranged  that  the  terreplein  shall  be  defiled  from  the 
enemy's  lodgment  on  the  crest  of  the  salient  place  of  arms. 
This  arrangement  necessarily  places  the  terre[)lein  between 
the  traverses  on  different  levels;  small  ramps  will,  there- 
foiT,  be  necessary  to  pass  from  one  level  to  the  other. 
They  are  placed  at  the  defiles. 

41!t...The  salient  place  of  arms  is  inclined  for  the  pur- 
pose of  partially  defiling  it  from  the  trench  cavalier. 

420. ..Finally,  the  traverses  are  sustained  on  the  side  of 
the  countei'scarp  by  a  profile  wall,  which  is  the  prolonga- 
tion of  the  counterscarp  wall  ;  and  they  are  terminated  at 
the  other  extremity  In'  a  wall,  so  as  to  make  the  defile  con- 
venient as  a  communication. 

421. ..Counterscarps  of  tfie  B.astion  .\nd  Dkmilt'ne. 
Having  determined  the  relief  of  the  covered-way  cre.sts, 
which,  it  may  be  observed,  is  such  tliat  they  mask  all  the 
masonry  of  the  scarps,  and,  at  the  same  time,  arc  so  low 


138  noizet's  method. 

that  ail  ciieiuy  cannot,  by  the  ordinary  methods  in  use, 
obtain  a  phinging  tire  from  them  upon  the  terrepleiiis  of 
the  works  in  their  rear,  the  position  of  tlie  counterscarp 
crests  can  now  be  fixed. 

422. ..The  top  of  tlie  counterscarp  wall  should  be  at  least 
8  feet  below  the  planes  of  the  interior  crest  of  the  covered- 
way,  and  the  height  of  the  wall  for  the  body  of  the  place 
should  not  exceed  24  feet,  and  for  the  demilune  it  may  be 
reduced  to  18  feet.  These  dimensions  will,  therefore,  be 
assumed,  as  the  greatest  that  can  be  allowed  with  a  proper 
regard  to  economy.  And  a  continuous  wall  of  these 
heights  may  be  regarded  as  a  powerful  auxiliary  obstacle, 
in  securing  the  works  from  all  attempts  at  surprise. 

423.. .Adopting  the  limit  of  24  feet  for  the  counterscarp 
of  the  bastion,  it  will  be  seen  that  the  bottom  of  the  ditch 
at  the  foot  of  this  wall  is  higher  than  at  the  foot  of  the 
scarp  wall  of  the  bastion  face ;  and,  as  the  bottom  of 
the  ditch,  at  the  extremity  of  the  double  caponniere,  has 
already  been  determined,  these  different  levels  must  be 
connected  by  planes,  combined  in  the  most  simple  manner. 

424...CuNETTES  AND  BOTTOMS  OF  THE  DiTCJiES.  Tls.  4  and 
5.  A  cunette,  4,0  yards  wide  at  top,  and  3  feet  deep,  is 
made  in  the  main  ditch  to  serve  as  a  drain.  A  ('(droi,  or 
small  arch  of  masonry,  is  made  under  the  double  capon- 
niere, connecting  the  cunette  on  the  opposing  sides  of  it. 
The  cunette  is  placed  parallel  to  the  bastion  face ;  the  bot- 
tom of  the  ditch  having  a  slope  of  1.50  feet  from  the  foot 
of  the  scarp  wall  to  the  edge  of  the  cunette,  and  a  slope 
from  the  opposite  edge  up  to  the  foot  of  the  counterscarp 
wall.  These  details  will  be  best  understood  by  referring  to 
ris.  4,  5,  Figs.  1.  The  slopes  here  given  serve  to  keep  the 
bottom  of  the  ditch  dry;  they  assist  in  rendering  the 
breach,  made  in  the  bastion  face,  rather  steeper  than  if  the 
bottom  were  horizontal ;  and,  in  the  passage  of  the  ditch, 
the  enemy's  work  is  thus  more  exposed  than  if  the  bottom 
were  not  sloped  from  the  foot  of  the  counterscarp  wall  to 
the  cunette. 

The  demilune  ditch  is  arranged  upon  similar  principles. 


noizet's  method.  139 

A  cnnette  and  culvert  arc  placed  in  it,  to  convey  the  rain- 
water from  it  into  tlic  main  ditch. 

425... Planes  of  the  Glacis.  The  glacis  of  the  covered- 
way  may  now  he  considered.  One  principle  is  chiefly  to  be 
attended  to  in  disposing  the  dilferent  planes  of  the  glacis. 
They  should  all  be  swept  by  the  artillery  fire  of  tlic  works 
immediately  in  their  rear,  and  by  the  musketry  tire,  at  least, 
of  the  bastion  face. 

426... The  glacis  of  the  l)astion  cov'cred-way  should  be 
swc[)t  by  the  artillery  of  the  bastion  face. 

427. ..The  glacis  of  the  re-entering  place  of  arms  should 
be  swept  by  the  lire  from  its  redoubt. 

428. ..The  glacis  of  the  demilune  offers  more  difficulty  in 
its  arrangement,  owing  to  the  cremaillere  form  of  the  in- 
terior crests.  The  best  method  seems  the  following:  planes 
are  passed  through  each  long  branch,  so  as  to  be  swept  by 
the  artiller}'  fire  of  a  portion  of  the  face  of  the  demilune ; 
these  are  connected  by  another  series  of  planes,  which  are 
passed  through  the  salient  point  of  each  crotchet,  below 
the  plane  of  musketry  fire,  of  at  least  one-half  of  tlie  bas- 
tion face;  and  below  that  of  artillery  fire,  of  a  part  of  the 
demilune  face. 

429... It  will  be  readilj'  seen,  from  the  nature  of  this 
problem,  that  it  admits  of  many  solutions.  In  selecting 
among.st  them,  the  following  considerations  may  serve  as 
guides.  When  the  planes  of  the  glacis  have  a  very  gentle 
slope,  they  are  better  seen  by  the  works  in  their  rear;  but 
the  construction  is  more  expensive,  on  account  of  tiie 
greater  quantity  of  embankment. 

430... When  the  slope  is  more  steep,  the  enemy's  works 
on  the  glacis  are  better  exposed  to  the  reverse  views  of  the 
collateral  works,  altiiough  not  so  well  seen  by  those  directly 
in  rear  of  the  glacis;  but  the  quantity  of  embankment  is 
smaller. 

431. ..Outlets,  on  Sortie  Passaues.  To  communicate 
from  the  eovered-way  with  the  glacis,  an  outlet  or  sortie  pas- 
sarje  is  cut  in  the  least  exposed  face  of  the  re-entering  place 
of  arms;  and  one,  also,  on  the  long  branch,  between  the  3d 


140  noizet's  method. 

and  4tli  traverses.  Tlicy  are  from  3.30  to  4.0  yards  wide. 
The  cut  is  about  6  feet  in  depth,  the  earth  heinjij  sustained 
on  each  side  by  a  profile  wall.  Tlie  bottom  of  it  is  a  ramp 
leading  from  the  terreplein  of  tlie  covered-way  to  the  top  of 
tlie  glacis.  As  the  outlet  is  closed  by  a  barrier,  it  sliould 
be  arranged  at  the  bottom,  to  allow  the  barrier  free  play  in 
opening  and  shutting. 

432. ..Communications.  Tliere  is  no  i>art  of  a  fortiticatiou 
wliere  more  care  and  judgment  are  required  than  in  the 
dispositions  made  to  communicate  from  the  interior  with 
the  outworks.  The  safety  of  the  besieged  essentially  de- 
pends on  a  proper  disposition  of  the  conmiuuications,  whicli 
should  afford  every  facility  for  offensive  movements,  and,  at 
the  same  time,  a  secure  and  easy  means  of  retreat.  This 
subject  has  been  treated  with  peculiar  care  by  Noizet 

433... Besides  the  ramps,  which  have  already  been  ex- 
plained, posterns  and  stairs  form  a  }iart  of  the  system  of 
communication. 

434... Posterns,  as  already'  has  been  stated,  are  arched 
comruunications  of  masonry,  made  under  the  rampart  or 
terreplein.  When  these  coninninications  are  required  for 
the  })assage  of  artillery,  they  should  be  at  least  10  feet  wide, 
and  8  feet  high  under  the  crown  or  key  of  the  arch.  "When 
for  infantry,  they  may  be  reduced  to  4  feet  in  width,  and  6 
feet  in  height,  under  the  key.  The  arch  of  the  postern  is 
generally  a  semi-circle,  or  what  is  called  a  full  centre  arch. 
To  l»(i  bonih-proof  it  should  be  at  least  3  feet  thick  through 
the  masonry  of  the  arch,  and  be  covered  by  at  least  from  3 
to  4.50  feet  of  earth. 

435. ..Stairs  are  only  used  in  situations  where  ramps  can- 
not be  placed;  as  for  example,  to  communicate  with  the 
interior  of  works,  the  gorges  of  which  are  revetted. 

Each  step  is  generally  formed  of  a  single  block  of  stone, 
which  is  2.0  yards  long  in  the  clear,  0.30  yard  in  width,  and 
0.20  yard  high.  From  these  dimensions  of  the  height,  or 
rise,  and  width,  or  tread,  of  each  step,  we  obtain  the  follow- 
ing formula  for  the  base  of  a  Jiiyht  of  steps,  when  the  height 
between  the  two  landings  is  given,  |  // — 0.30— base. 


xoizet's  method.  141 

Stairs  are  not  so  convenient  as  ramps;  and  they  are, 
moreover,  liable  to  l)e  easih'  put  out  of  order  b}-  the  effects 
of  shot  and  shells. 

436... Communication  of  the  Enceinte  with  the  Ditch. 
The  postern  of  tlie  enceinte  leads  through  the  middle  of 
the  curtain,  descending  from  the  plane  of  sight  to  the  ditch. 
The  inclination  of  the  bottom  should  never  exceed  |.  Tlic 
bottom  should  not  come  out  upon  a  level  with  the  bottom 
of  the  ditch,  but  about  6  feet  above  it — a  wooden  ramp 
being  used  to  descend  from  the  postern  to  the  bottom  of 
the  ditch. 

The  width  of  this  postern  should  be  12  feet,  both  on 
account  of  the  greater  circulation  through  it,  and  because 
it  may  be  used  as  a  bond)-proof  shelter  for  the  troops  on 
duty. 

The  entrance  to  this  postern,  both  toward  the  ditch  and 
the  interior,  is  b}'  door-ways;  one  through  the  scarp  wall, 
which  closes  the  postern  toward  the  ditch,  and  one  through 
a  vertical  wall  of  masonry,  at  the  extremity  of  the  enceinte 
terreplcin,  which  closes  the  mouth  of  the  postern  toward 
the  interior.  The  earth  of  the  rampart-slope  is  cut  away, 
to  leave  the  passage  to  the  postern  free.  The  sides  of  the 
cut  are  sustained  b}'  wing  walls,  which  make  a  small  angle 
with  the  vertical  wall  of  the  postern  mouth.  The  door-way 
may  be  7.0  feet  wide,  and  7. .50  feet  high.  The  postern  itself 
being  10  feet  under  the  key. 

For  more  security,  a  partition  wall,  with  a  door-way,  is 
sometimes  made  across  the  postern,  about  the  middle  point. 
Tlic  leaves  of  the  folding-doors  here  liave  loop-holes  to  fire 
upon  an  enemy,  should  he,  by  a  surprise,  gain  possession  of 
the  exterior  door-way. 

487... Communication  with  the  Tenaille.  A  postern,  for 
the  passage  of  artilk'ry,  is  made  under  the  tenaille,  and 
leads  to  the  double  caponniere.  Two  stairs  are  placed  at 
the  gorge  of  the  tenaille,  to  communicate  with  its  terre- 
plcin. 

488... Communication  with  the  Terreplein  and  Ditch 
of  the  Demilune  Redoubt.     Two  stairs  are  placed  at  the 


142  xotzet's  method. 

gorge  of  the  demilune  redoubt,  to  communicate  witli  its 
terreplein.  A  postern  for  artillery  leads  from  the  main 
ditch  to  the  ditch  of  the  redoubt,  under  its  flank,  for  the 
communication  between  the  main  ditch  and  the  demilune. 

43y...COxMMUNICATION  FROM  THE  EnCEINTE  DiTCH  WITH  THE 

Exterior.  To  communicate  with  the  covered-ways,  a  ramp 
of  earth  sustained  by  walls  is  placed  along  the  wall  that 
terminates  the  demilune  and  its  redonbt.  This  ramp  is 
separated  from  the  extremity  of  the  face-cover  by  a  cut 
4.30  yards  wide. 

440... Communication  with  the  Demilune  Cut.  The 
communication  with  the  work  behind  the  demilune  cut  is 
by  a  ppstern  and  stairs  for  infantry,  wliich  lead  from  a 
}K)int  on  the  ramp  just  described  to  the  terreplein  of  the 
-^vork — passing  in  a  winding  direction  under  the  terreplein 
and  j)arapet  of  the  work. 

441... Communications  of  the  Redoubt  of  the  Re-enter- 
ing Place  of  Arms,  etc.  The  passage  behind  tlie  single 
caponniere,  in  the  demilune  ditch,  has  already  been  de- 
scribed. The  passage  leads  to  a  postern  for  artillery,  made 
through  the  face  of  the  redoubt,  to  its  ditch.  From  the 
ditch,  a  ramp  for  artillery  leads  to  the  terreplein  of  the  i-e- 
entering  place  of  arms.  At  the  angle  of  the  redoubt  on 
the  demilune  ditch,  stairs  are  placed  to  ascend  to  its  ditch  ; 
a  ramp  foi-  infantry  leads  from  the  ditch  on  this  side  to  the 
terrei)lein. 

442. ..To  ascend  to  the  terreplein  of  the  redoubt,  a  small 
postern  for  infantry  is  made  through  the  face  to  the  ditch, 
being  placed  alongside  the  postern  just  described;  from 
this,  a  winding  postern  and  stairs  lead  to  the  terreplein  of 
the  redoubt. 

The  foregoing,  with  what  has  been  said  respecting  the 
capon nieres,  traverse  deiiles,  etc.,  completes  the  description 
of  the  communications  of  the  front.  This  subject  may  be 
closed  with  a  recapitulation  of  the  principal  conditions 
which  should  regulate  every  system  of  communications. 

443... Remarks  on  the  Communications.  1st.  The  commu- 
mcations  should  never,  from  their  position,  com-promisc  the  safetij 
of  the  enceinte. 


noizet's  method.  143 

Frequent  instances  could  be  cited  of  works  wliich  have 
been  surprised  by  an  enemy  obtaining  possession  of  the 
gates.  Therefore,  too  many  })recantions  cannot  be  taken  to 
secure  the  principal  outlet  from  the  body  ot  the  place  from 
similar  attempts.  It  is  on  this  account  tliat  the  postern  in 
the  body  of  the  place  is  arranged  as  has  been  described,  to 
frustrate  any  sudden  attack  tliat  might  be  made  upon  it. 

444... 2d.  The  cormmmications  should  admit  of  a  convenient 
circidation  of  the  besieged. 

To  subserve  this  purpose,  the  dimensions,  slopes,  etc.,  of 
the  posterns,  ramps,  and  other  similar  Avorks,  shouhl  be  con- 
venient for  the  service  to  which  they  are  applied  ;  and  they 
should  be  placed  in  such  positions  as  lead  directly  to  the 
point  to  be  arrived  at.  In  examining  the  form,  dimensions 
and  position  of  the  ramps,  etc.,  of  the  front,  it  will  be  found 
that  these  conditions  are  well  satisfied. 

445 ...  3d.  The  position  chosen  for  any  commanication  shoidd  be 
such,  that  when  an  enemy  yets  2^ossession  of  it,  he  may  obtain  no 
advantaye  by  it. 

To  be  useless  to  an  enemy,  the  communication,  Avhen  in 
his  possession,  should  not  offer  a  shelter  for  his  works  ;  nor 
enable  him  to  carry  them  on  with  more  ease.  This  end 
will  be  obtained  by  placing  the  communications  in  a  posi- 
tion to  be  enfiladed  by  the  fire  of  the  works  in  their  rear; 
and  so  arranging  them  as  to  preserve  the  counterscarp  wall 
unbroken,  by  which  means  any  facility  for  attempts  at  sur- 
prise will  be  avoided. 

4th.  The  commmncations  shoidd  be  covered  from  every  point 
where  an  enemy  might  establish  himself,  during  the  whole  period 
that  they  can  be  of  service  to  the  besiegers ;  and  they  should  be 
swept  by  the  fire  of  the  enceinte. 

Without  these  precautions,  an  cnony  miglit  cut  oflt'  all 
communication  fi'om  the  enceinte  with  the  outworks;  and 
in  cases  of  retreat,  the  troops  could  not  derive  any  assist- 
ance from  the  enceinte,  if  he  attempted  to  press  upon  them. 

44<)...In  covering  the  communications,  existing  masses 
should,  when  convenient,  be  used,  whi<.'h  form  a  i>art  of  tlie 
general  arrangement  of  the  works.     Examples  of  this  are 


144  noizet's  method. 

shown  ill  the  manner  in  which  the  deboiirhe  fvom  the  (h)iihle 
caponniere,  and  also  those  from  the  traverse  defiles,  are 
covered.  In  the  first  case,  hy  the  angle  of  the  counterscarp 
wall  and  the  salient  of  the  bastion;  and  in  the  second,  by 
the  angle  of  the  profile  walls  of  the  traverses  and  the  demi- 
lune salient.  Sometimes  a  special  mask  has  to  be  raised, 
an  exam})le  of  which  is  seen  in  the  traverse  at  the  gorge  of 
the  redoubt  of  the  re-entering  place  of  arms,  which  covers 
the  door  of  the  postern  of  the  redoubt. 

447... 5th.  The  communications  should  he  so  j)laced  as  not  to 
compromise  the  retreat  of  the  troops. 

This  is  effected  by  placing  the  communication  in  the 
re-enterings,  which  are  the  most  secure  points,  as  an  enemy 
to  arrive  at  them  will  liavc  to  brave  a  powerful  column  of 
flank  fire.  Barriers,  gates,  and  movable  bridges  of  timber 
should  be  placed  at  suitable  points,  to  cut  off  one  commu- 
nication fr(^m  another;  and  thus  arrest  the  progress  of  a 
pursuing  enemy. 

448... Gth.  Finally,  each  worJc  sJiould  be  independent  of  every 
communication,  except  the  one  destined  for  its  particular  use. 

This  is  an  important  object,  as  it  prevents  an  enemy, 
should  he  succeed  in  gaining  possession  of  a  communica- 
tion leading  through  it,  from  seizing  upon  the  work  itself. 
Examples  of  this  arrangement  are  shown  in  the  postern, 
through  the  face  of  the  redoubt  of  the  re-entering  place  of 
arms,  which  leads  to  the  exterior,  and  which  is  not  con- 
nected with  the  small  postern  destined  for  the  service  of 
the  redoubt  itself;  also,  in  the  postern  leading  from  the 
main  ditch  to  that  of  the  demilune  redoubt,  for  the  service 
of  the  demilune.  This  postern  does  not  interfere  with  the 
safety  of  the  redoubt.  • 

449..  By  examining  the  communications  of  the  front, 
generally,  according  to  these  conditions,  it  will  be  found 
that  their  arrangement  is  as  judicious  as  the  nature  of  the 
problem  seems  to  admit. 

450... Interior  Retrenchments.  The  front,  as  it  has  now 
been  described,  appears  to  be  of  a  character  to  protract  the 
siege  to  the  longest  duration.     AVhen,  however,  a  broach  is 


I 


noizet's  method.  145 

made  in  tlie  enceinte,  although  military  usage  and  a  point 
of  honor  require  of  the  garrison  to  sustain,  at  least,  one 
assault,  the  consequences  of  defeat  are  of  too  serious  a 
character  to  expect  such  an  eftbrt,  unless  a  place  of  safety 
is  provided,  into  which  the  garrison  may  retreat,  after 
defending  the  hreach,  and  obtain  an  honorable  capitulation. 
On  this  account,  and  also  to  lengthen  the  defence,  interior 
retrenchments  are  made  in  the  bastions.  These  works 
may  be  either  of  a  temporary  or  permanent  character;  but 
it  is,  generally,  conceded  that  the  latter  class  alone  otters  a 
serious  obstacle  to  the  enemy.  The  former,  moreover, 
requires  that  the  bastion  should  be  full,  and  that  the  re- 
trenchment should  be  thrown  up  during  the  siege  —  an 
undertaking  of  great  difficulty,  both  from  the  annoyance 
of  the  enemy's  fire  and  the  fatigued  state  of  the  garrison 
occasioned  by  its  ordinary  duties. 

451... Therefore,  onl}'  the  permanent  interior  retrench- 
ments with  a  revetted  scarp  and  counterscarp  will  be  given; 
and  which  may  be  regarded  as  an  element  of  a  regularly 
fortified  front. 

452...Noizet,  like  Cormontaingne,  proposes  four  classes 
of  interior  retrenchments.  1st.  Those  that  rest  against  the 
faces  of  the  bastions.  2d.  Those  that  rest  against  the 
flanks.  3d.  Those  that  rest  against  two  adjacent  curtains. 
4th.  Those  that  comprehend  several  bastions. 

453... First  class  resting  on  the  Faces.  PI.  6,  Figs. 
1,  2,  and  A,  B,  Fig.  3.  The  first  class  may  be  either  the 
form  of  a  cav^alier,  shut  in  by  cuts  across  the  bastion  faces, 
or  an  inverted  redan ;  or,  finally,  if  the  bastion  is  very 
open,  a  small  bastion  front.  Of  this  class,  the  cavalier  has 
been  general I3'  employed.  The  cavalier  receiving  a  relief 
80  great  as  to  give  it  a  plunging  fire  upon  the  enemy's 
works  on  the  glacis  of  the  bastioned  covered-way ;  whilst 
the  interior  of  the  bastion,  in  advance  of  the  cavalier  ditch 
and  of  the  cuts  or  ditches  across  the  bastion  terreplein, 
between  the  scarps  of  the  bastion  and  cavalier,  is  swept, 
and  the  breach  that  might  be  made  in  the  bastion  salient 
can  be  defended  from  the  parapets  ])chind  the  cuts.  These 
10 


14G  noizet's  method. 

parapets,  witli  the  portions  of  tlie  cavalier  faces  in  advance 
of  tlieni,  forming  the  interior  retrenchment. 

454. ..This  class  i)rescnts  the  advantages  of  defending  the 
l)rea('h  within  a  short  distance,  and  by  enclosing  the  tianks 
of  the  bastion  within  tliem,  they  preserve  the  flanking 
arrangements  of  the  body  of  the  place  until  the  retrench- 
ment is  carried.  The  principal  objection  to  them  is  that, 
by  a  breach  made  at  the  shoulder  angle,  the  enemy  can 
turn  them. 

455... Second  class  resting  against  the  Flanks.  PI,  G. 
Figs.  4  and  C.  The  second  class  may  be  of  an  inverted 
redan,  or  a  small  bastion  front ;  or,  finally,  of  a  redan  rest- 
ing against  the  middle  of  the  flanks,  its  faces  having  such 
a  direction  that  its  ditch  may  be  swept  by  the  fire  of  the 
flanks  of  the  adjacent  bastions. 

The  last  form  admits  of  defending  the  breach  within  a 
short  distance;  it  preserves  also  the  flanking  arrangements 
of  the  enceinte,  and  can  oidy  be  turned  by  a  breacli  made 
in  the  curtain.  To  sweep  its  ditch  from  the  opposite  flank, 
it  will  be  necessary  to  cut  down  a  }>art  of  the  scarp  wall  of 
the  flank  on  which  the  ditch  rests,  which  will  nudce  the 
height  of  the  wall  less  than  11.0  yards,  and  soniewhat 
expose  the  enceinte  to  escalade. 

456...TUIRD    CLASS    RESTING    ON    TWO    ADJACENT    CURTAINS. 

PI.  6,  Fig.  4,  D.     The  third  class  is  usually  of  the  form  of 

a  bastioned  front;  but  as  the  fire  of  its  faces  would  be 

masked  by  the  curtain  of  the  enceinte,  it  is  generally  best 

to  construct  the  front  simply  with  a  curtain  and  two  flanks. 

This  class  being  thrown  farther  from  the  salient  of  the 

bastion,  does  not  defend  the  breach  so  directlv  as  the  two 

...  • 

preceding;  but  its  position  is  stronger,  and  will   force  an 

enemy  to  employ  more  means  to  cany  it.  From  its  dimen- 
sions, it  will  require  more  space  on  the  interior,  and  will 
be  also  more  expensive  than  either  of  the  preceding  forms. 
457... Fourth  class  enclosing  several  Fronts.  The 
fourth  class,  which  is  placed  in  the  rear  of  several  bastions 
of  the  enceinte,  or  properly,  several  fronts,  is  a  kind  of 
second  enceinte  within  the  first.     An  arrangement  of  this 


noizet's  method.  147 

character  would,  of  course,  require  a  peculiar  locality,  and 
would  seldom  find  an  ajtplication. 

458... Cavalier  with  Cuts  in  the  Bastion  Faces.  PI.  6, 
Fi^s.  1,  2.  The  faces  of  this  work  are  parallel  to  those  of  the 
bastion  in  which  it  is  placed;  its  ditch  should  be  about  18 
feet  below  the  bastion  terreplein;  its  scarp  wall  about  24 
feet  high.  And  it  ma\'  be  here  observed  that  all  interior 
retrenchments,  to  oppose  a  serious  obstacle  to  an  enemy, 
should  have  rcvetements  of  about  these  dimonsions. 

459. ..The  interior  crest  of  the  face  should  be  so  hio-h 
that  the  line  of  lire,  from  the  salient  of  the  cavalier  to  the 
salient  of  the  bastion  covered-way,  shall  pass  above  the 
bastion  salient.  By  placing  the  counterscarp  of  the  cavalier 
at  14.0  yards  from  the  interior  crest  of  the  bastion — allow- 
ing 11.0  yards  for  the  width  of  the  ditch,  and  making  the 

bottom  of  the  ditch  18  feet  below  the  bastion  terreplein 

it  will  be  found  that  the  reference  of  the  bottom  of  the 
ditch  will  be  (58.50);  the  scarp  wall  being  24  feet  high,  the 
reference  of  its  magistral  will  be  (82.50).  Now,  if  the 
reference  of  the  interior  crest  be  taken  at  (97.50),  or  15 
feet  above  the  magistral,  its  projection  will  be  at  33.16  feet, 
or  11.06 yards  from  the  magistral;  and  as  l)oth  the  lines  are 
horizontal,  parallel  to  it.  ]J>rawing,  then,  three  lines  parallel 
to  the  bastion  interior  crest,  at  the  distance  above  men- 
tioned, the  projections  of  the  counterscarp,  scarp  and  in- 
terior crest  of  the  cavalier  are  obtained.  The  position  here 
given  to  tlie  interior  crest  of  the  face  will  satisfy  the  con- 
dition tirst  laid  down. 

460. ..The  interior  crest  of  the  flank  is  also  horizontal; 
its  reference,  therefore,  is  (97.50);  the  direction  of  the  flank 
is  perpendicular  to  tlie  line  of  defence  of  the  bastion  ;  the 
flank,  moreover,  is  not  revetted  like  the  face,  but  is  ter- 
minated by  prolonging  its  exterior  slope  to  the  bastion 
terreplein ;  the  lowest  point  of  the  foot  of  this  exterior 
slope  will,  therefore,  be  about  (73.00),  the  reference  of  the 
bastion  terreplein  at  the  extrcmit}-  of  its  flank;  the  least 
width  of  the  bastion  terreplein,  between  it«  flank  and  that 
of  the  cavalier,  should   be  14.0  yards.     If,  then,  from  the 


148  noizet's  method. 

interior  angle  of  tlie  curtain,  with  a  radius  of  14.0  yards, 
an  arc-  be  described,  and  a  tangent  be  drawn  to  this  arc, 
perpendicuhir  to  the  line  of  defence,  this  tangent  may  be 
taken  as  the  horizontal  of  the  exterior  slope  of  the  cavalier 
flank,  whose  reference  is  (73.0);  the  interior  crest  of  the 
flank  is  drawn  parallel  to  this  horizontal,  and  at  41.16  feet, 
or  13.72  yards  from  it;  which  will  be  the  distance  found  by 
calculation,  the  thickness  of  the  parapet  being  20  feet,  the 
superior  slope  ^,  and  the  exterior  slope  |. 

461... The  length  of  the  flank  is  found  by  drawing, 
through  the  angle  of  the  curtain,  a  line  parallel  to  the 
line  of  defence;  and  where  it  cuts  the  interior  crest  of  the 
flank,  will  be  the  extremity  of  the  flank. 

462... To  terminate  the  gorge  of  the  cavalier,  a  plane 
of  {  is  passed  through  the  extreme  points  of  the  interior 
crest  of  its  flanks.  A  passage  of  4.30  yards  is  left  on  the 
'  bastion  terreplein,  at  the  gorge  of  the  cavalier,  to  commu- 
nicate with  it;  and  also  to  preserve  an  uninterrupted  com- 
munication between  the  two  adjacent  curtains.  A  ramp, 
3.30  yards  wide,  with  a  slope  of  ^,  leads  from  the  gorge  of 
the  cavalier  to  its  terreplein.  This  ramp  is  generally  placed 
along  the  capital  of  the  bastion. 

463... Cuts  in  the  Bastion  Faces.  PI.  6,  Figs.  1,  2.  To 
determine  the  cut  across  the  bastion  face,  a  distance  of  13.0 
yards  is  set  oft'  from  the  shoulder  angle  of  the  bastion, 
along  its  interior  crest;  from  this  point  a  line  is  drawn, 
making  an  angle  of  100°  with  the  interior  crest;  this  line 
being  produced  to  intersect  the  magistral  of  the  cavalier 
face,  is  the  interior  crest  of  the  parapet  behind  the  cut. 
The  reference  of  this  line  where  it  intersects  the  magistral 
is  (82.50),  the  reference  of  the  other  extremity  being  (84.0): 
it  is  held  in  the  same  plane  with  the  portion  of  the  interior 
crest  of  the  bastion,  between  the  shoulder  angle  and  the 
point  at  13.0  yards  from  it;  the  reference  of  the  shoulder 
angle  remaining  as  already  found;  it  will  be  seen  that  the 
plane  of  these  two  lines  produced,  passes  3  feet  above  the 
bastion  salient.     The  thickness  of  parapet  is  only  12  feet. 

464... The  magistral  of  the  scarp  of  the  cut  is  horizontal, 


J 


NOIZET  S    METHOD. 


149 


its  reference  Leing  (76.50).  From  the  preceding  data,  its 
position  is  easily  determined.  A  line  drawn  parallel  to  the 
magistral,  and  at  6.60  yards  from  it,  will  be  the  connter- 
scarp  of  the  cut.  The  counterscarp  wall  of  the  cut  is 
carried  up  to  the  top  of  the  bastion  face,  and  forms  a  profile 
wall  to  sustain  the  earth.  The  scarp  wall  of  the  cut  is 
of  the  same  height  as  that  of  the  cavalier;  the  bottom  of 
the  cut  will,  therefore,  be  referenced  (52.50),  a  portion  of 
the  ditch  of  the  cavalier  face  has  the  same  reference;  this 
l)ortiou  is  fomid  by  holding  at  the  level  (58.50),  that  part  of 
the  bottom  of  the  ditch  toward  the  salient  which  can  be 
swept  by  the  lire  of  the  parapet  behind  the  cut;  placing 
the  bottom  of  the  remaining  portion  toward  the  cut,  on  the 
same  level  as  the  bottom  of  the  cut,  or  at  the  reference 
(52.50);  the  two  levels  being  separated  by  a  vertical  wall 
6  feet  high,  which  retains  the  earth  of  the  upper  level. 

465... This  arrangement  of  the  ditch  of  the  cavalier  sub- 
jects only  a  part  of  it  to  the  fire  of  the  parapet  behind  the 
cut.  By  placing  the  door  of  the  postern  that  leads  into  the 
cavalier  ditch,  at  the  point  where  the  vertical  wall  separates 
the  two  levels,  it  will  be  partially  covered  from  the  enemy's 
lodgment  on  the  bastion  tcrreplein. 

466... The  object  of  the  cut  is  similar  to  the  one  in  the 
demilune  face;  it  confines  the  enemy  to  the  salient  part  of 
the  bastion,  preventing  him  from  extending  his  works  along 
the  bastion  terreplein,  to  turn  the  cavalier  by  its  gorge;  so 
that  to  obtain  possession  of  this  work,  he  must  make  a 
breach  in  its  face. " 

467... There  is  a  dead  space  in  the  cavalier  ditch  through- 
out the  lower  level,  which  might  ofter  some  advantages 
were  the  enemy  to  attempt  to  carry  the  parapet  of  the  cut 
by  escalade.  To  remedy  this  defect,  it  has  been  proposed 
to  place  a  erenated  gallery  behind  the  scarp  wall  of  the  cut, 
to  flank  the  entire  ditch. 

468. ..The  disposition  of  the  cavalier  and  cuts  within  the 
bastion  do  not  leave  sufficient  space  upon  the  terreplein  of 
the  latter  to  organize  a  covered-way.  But  in  the  retrench- 
ments of  open  bastions,  resting  on  the  flanks  or  curtains, 


150  CHASSELOUP'S    METHOD. 

to  which  the  form  of  a  teniiille,  or  a  small  bastioned  front 
is  given,  a  covered-way,  with  a  re-entering  place  of  arms, 
closed  by  traverses,  can  be  organized,  which  will  give  con- 
siderable additional  confidence  and  security  in  the  defence 
of  the  breach  in  the  bastion  with  the  bayonet  —  as  this 
covered-way  will  cover  the  retreat  of  the  troops,  guarding 
the  breach,  into  the  ditch  of  the  enceinte — whereas,  when 
the  counterscarp  is  not  secured  in  this  way,  the  retreating 
body  run  the  risk  either  of  being  cut  off  or  of  having  the 
enemy  follow  so  closely  on  their  heels  as  to  force  their  way 
into  the  retrenchment,  and  deprive  the  defence  of  this  last 
resort  for  making  favorable  terms  of  surrender. 

469... The  organization  of  these  covered-ways  presents  no 
peculiarity.  They  should,  as  far  as  practicable,  be  defiled 
from  the  besieger's  lodgments  with  the  bastion  assailed. 


(l|hHj)Sd0ii|j'B  P^ithol 


470...Chasseloup  was  one  of  the  most  distinguished  engi- 
neers under  Napoleon,  and  had  the  principal  charge  of  the 
fortifications  constructed  by  the  French  in  the  north  of 
Italy,  whilst  it  was  a  part  of  the  French  empire.  His 
views  are  to  be  gathered  chiefly  from  some  short  memoirs 
published  without  his  name,  in  which  are  to  be  found  many 
of  the  leading  ideas  of  several  later  engineers  of  the  French 
school,  and  what  is  now  termed  the  German  school. 

471... Chasseloup  adheres  to  the  bastioned  system  as  the 
basis  of  his  enceinte,  in  which,  however,  he  proposes  the 
following  modifications  of  the  combinations  usually  admit- 
ted by  his  predecessors,  viz:  1st,  in  giving  a  greater  length 
to  the  exterior  side,  which  he  proposes  to  vary,  if  neces- 
sary, between  440  and  660  yards;  2d,  in  so  arranging  the 
plan  of  his  enceinte  that  the  portion  of  the  bastion  faces 


CHASSELOUP'S    METHOD.  151 

toward  the  salients  sliall  be  covered  b}"  the  demib.nies  from 
enfilading  views;  3d,  in  throwing  back  the  parapets  of  cer- 
tain portions  of  his  front,  which  are  exposed  to  be  breached, 
so  far  to  the  rear  that  when  the  scarp  wall  is  battered  down 
the  breach  will  still  be  closed  by  the  parapet;  4th,  in  ar- 
ranging the  tenaille  with  casemated  flanks  solely  for  ditch 
defence,  which  are  covered  by  a  mask  from  the  counter- 
batteries  at  the  salient  of  the  bastioned  covered- way ;  whilst 
by  openings  pierced  in  the  mask,  the  fire  of  the  flanks  can 
be  directed  on  the  point  to  be  attained;  5th,  in  placing  in 
the  main  ditch  a  casemated  capon niere  to  obtain  a  reverse 
fire  on  the  breaches  in  the  bastion  faces;  6th,  in  isolating 
the  main  ditch  from  the  ditches  of  the  outworks,  covering 
it  and  the  caponniere  b}^  a  covered-way,  organized  with  case- 
mated  traverses  and  redoubts  for  defence;  7th,  in  detaching 
the  demilune  from  the  enceinte,  throwing  it  so  far  forward 
as  to  cover  the  bastion  faces  from  enfilade,  and  in  placingin 
the  demilune  a  casemated  redoubt  to  procure  reverse  views 
on  the  approaches  on  the  bastion  salients;  8th,  in  organiz- 
ing the  demilune  covered-way  in  the  same  manner  as  that 
of  the  enceinte ;  9th,  in  placing  within  his  bastions  strong 
interior  retrenchments,  with  casemated  shelters  for  the  ar- 
tillerj^  in  reserve,  and  defensive  casemated  quarters  for  the 
garrison. 

472... Plan.  The  exterior  side,  PI.  17,  XF,  is  taken  at 
580  metres  (French);  the  perpendicular,  ZU,  is  \  of  XY; 
a  portion  of  each  face,  JTm,  Ym'^  equal  to  60  m.  lies  on  X  Y; 
from  m  and  rii'  lines  of  defence  are  drawn  through  U^  on 
which  the  interior  portions  of  the  faces,  each  160  m.,  are 
set  oft";  the  flanks  are  drawn  pei-pendieular  to  the  lines  of 
defence,  and  are  about  48  m. 

478. ..The  tenaille  is  separated  from  the  curtain  by  a  ditch 
of  10  m.,  and  from  tlie  flanks  b}'  ditches  of  15  m.  The  rear 
portion,  c,  Figs.  1,  2,  of  the  flank,  is  casemated  for  three 
guns,  each  casemate  being  open  to  the  rear;  an  open  court, 
e,  of  a  rectangular  shape,  is  left  opposite  the  casemates,  in 
front  of  which  is  the  mask,  d,  pierced  with  arched  open- 
ings, through  which  the  shot  from  the  casem.ated  guns  are 


152  CHASSELOUP'S    METHOD. 

directed.  The  gorge  of  the  tenaille  has  a  counterscarp 
gallery. 

474... The  salient,  S,  of  the  caponniere  in  the  main  ditch 
is  at  55  m.  from  Z,  on  the  exterior  side;  its  faces,  S,  F,  are 
65  m.,  and  directed  on  points  Q,  Q',  at  50  m.  from  the  bastion 
shoulder  angles ;  the  flanks  are  parallel  to  the  perpendicu- 
lar of  the  front,  and  60  m.  The  parapets  of  this  caponniere 
are  thrown  back  from  the  scarp  wall  to  increase  the  difii- 
cultj  of  the  breach ;  the  parapets  of  the  faces  being  higher 
than  those  of  the  flanks,  to  cover  them  from  enfilade  views. 
The  masonry  of  the  flanks  of  this  work  is  covered  by  a 
glacis,  y  z  f,  which  is  revetted,  leaving  ditches  of  5  m.  be- 
tween it  and  the  scarp  and  counterscarp  of  the  enceinte, 
and  of  10  m.  between  it  and  the  caponniere  flanks. 

475. ..The  counterscarp  of  the  main  ditch  is  20  m.  wide 
at  the  salients,  and  directed  on  the  flanks  of  the  caponniere 
af  points  5  m.  from  the  shoulder  angles.  The  ditch  of  the 
caponniere  at  the  faces  is  10  m.  wide. 

476... The  covered-way  has  a  re-entering  place  of  arms  at 
the  re-entering  between  the  counterscarps  of  the  enceinte 
and  caponniere  faces,  which  extends  to  within  50  m.  of  the 
front  S'.  A  salient  place  of  arms,  of  a  polygonal  form, 
like  that  of  the  demilune  covered-way,  but  not  represented 
on  Fig.  1,  is  arranged  in  front  of  each  bastioned  salient. 
Each  of  these  places  of  arms,  Fig.  4,  is  occupied  w^ith  a 
pol^'gonal  casemated  redoubt.  The  branches  of  the  cov- 
ered-way, between  the  places  of  arms,  are  broken  into  a 
cremaillere  line,  the  longer  branches  of  which,  prolonged, 
fall  within  the  bastion  salients.  Traverses,  either  casemated 
for  reverse  fires  or  of  the  ordinary  construction,  are  placed 
in  the  enlarged  portions  of  the  covered-way  formed  by  the 
long  and  short  branches  of  the  cremaillere.  The  directions 
of  the  crests  of  the  covered- way,  and  their  lengths,  are 
given  by  the  dimensions  on  the  plan. 

477... The  salient,  T,  of  the  demilune,  is  at  170  m.  from 
the  point  *S'',  on  the  caponniere  counterscarp ;  its  faces  are 
directed  on  points  j9,  j;',  at  100  m.  from  the  bastion  shoulder 
angles.     A  cut  of  5  m.  is  made  in  each  face  of  this  work 


CHASSELOUP'S    METHOD.  153 

at  70  m.  from  the  salient.  The  faces  are  prolonged  50  m. 
beyond  the  cut,  and  are  terminated  by  arcs  described  from 
the  shoulder  angles  of  the  demilune  redoubt  and  lines 
draAvn  from  these  centres  to  points  on  the  bastion  capitals, 
at  40  m.  in  advance  of  the  salient  place  of  arms.  Within 
the  salient  of  the  demilune  a  curved  traverse  is  arranged, 
with  countersloping  embrasures  for  howitzer  firing  along 
the  capitals,  in  rear  of  which  is  a  small  casemated  redoubt, 
B.     The  demilune  ditch  is  20  m.  wide. 

478... The  ditches  of  the  demilune  redoubt,  0,  are  18  m. 
wide  ;  the  faces  of  this  work  are  32  m. ;  its  flanks,  20  m. 
The  flanks,  Fig.  3,  are  casemated  for  2  guns.  The  gorge 
of  the  redoubt  is  a  small  bastioned  front.  The  faces  and 
flanks  have  an  open  defence  covered  by  a  parapet. 

479... The  demilune  covered-way  is  organized  like  that  of 
the  enceinte,  with  casemated  redoubts.  A',  B',  in  the  salient 
and  re-entering  places  of  arms.  Between  these  redoubts 
are  two  traverses,  a  6,  ab';  the  latter  covers  the  masonry  of 
the  redoubt.  A',  and  closes  the  re-entering  places  of  arms. 

480... The  glacis  of  the  enceinte  slopes  oft'  toward  the 
gorge  of  the  demilune  and  its  redoubt,  so  that  all  the  rear 
of  these  works  is  exposed  to  the  face  of  the  enceinte. 

481... Besides  the  ordinary  open  communications,  Chasse- 
loup's  front  is  organized  with  a  very  extensive  combination 
of  posterns  and  galleries  for  scarp  and  counterscarp  de- 
fences and  mines,  both  for  the  service  of  the  defences  of 
the  enceinte  and  of  the  outworks. 

482... The  principal  features  of  Chasseloup's  combina- 
tions consist  in  his  mode  of  closing  the  opening  for  breach- 
ing the  bastion  faces,  as  seen  in  Vauban's  fronts,  through 
the  demilune  ditches,  by  throwing  forward  the  demilune  as 
a  detached  work;  in  his  organization  of  his  covered  ways 
with  casemated  redoubts,  and  of  his  demilune  redoubt  with 
casemated  flanks  having  reveree  views  on  the  bastion  glacis. 
It  has  been  objected  to  the  position  he  gives  the  demilune 
that  botli  this  work  and  its  covered-way  are  exposed  to  be 
carried  by  an  open  assault  at  the  gorge,  in  which  case  its 
redoubt  would  readily  fall,  and  the  advantages  proposed  be 


154  HAXO'S    METHOD. 

lost;  also,  that  the  casemated  redoubts  in  the  covered-ways 
will  be  so  damaged  by  the  ricochet  fire  of  the  enfilading 
batteries  as  to  be  useless  when  the  covered-way  is  attacked. 


ia^eo's  flittlwd. 


483... General  Ilaxo  holds  the  first  rank  among  the  more 
recent  engineers  of  the  French  school.  Having  served 
under  Chasseloup  in  the  construction  of  the  fortifications 
of  !N"orthern  Ital}^,  he  subsequently  acquired  a  distinguished 
reputation  by  his  services  in  the  Peninsular  war,  where  he 
was  engaged  in  several  of  the  remarkable  sieges  of  that 
epoch,  and  he  finally  became  President  of  the  Board  of 
Engineers,  and  in  that  capacity  directed  several  of  the  most 
important  fortifications  of  recent  date  in  France. 

Nothing  of  General  Haxo's  views  on  the  subject  of  for- 
tification came  before  the  public  during  his  life.  The  front 
which  accompanies  this  description  he  had  engraved,  and 
copies  of  it  distributed  among  the  oflicers  of  his  corps,  but 
under  an  injunction  of  secrecy. 

484... Plan.  The  exterior  side,  CD,  of  the  enceinte, 
PI.  18,  is  393.48  yards;  the  lines  of  defence,  C H,  D  G,  are 
directed  on  the  point  D',  at  43.72  yards  from  C,  or  one- 
ninth  of  the  exterior  side;  the  faces  CE  and  D F^  are 
74.32  yards  ;  the  flanks  E  G,  F H,  are  perpendicular  to  the 
lines  of  defence.  •• 

485. ..The  tenaille  consists  of  a  curtain  and  flanks;  it  is 
revetted  only  on  the  exterior  of  the  two  flanks;  it  is  sep- 
arated from  the  curtain  of  the  enceinte  by  a  ditch  13.11 
yards  wide,  and  from  the  flanks  by  one  of  6.50  yards  :  the 
flanks  of  the  tenaille  are  about  3  feet  higher  than  its  cur- 
tain, and  are  arranged  for  three  sruns.  The  foot  of  the 
exterior  slope  of  the  tenaille  curtain  extends  76.5  yards  on 


HAXO'S    METHOD.  155 

each  side  of  C,  to  the  point  where  the  exterior  revetenient 
wall  of  the  flank  commences. 

486...Countergnar(ls  are  placed  in  front  of  the  bastions; 
the  ditches  between  them  and  the  bastions  being  16.39 
yards  wide  at  the  salient,  and  tlieir  counterscarps  being 
directed  on  a  point  D",  38.25  yards  from  C;  the  salients 
of  the  conntergnards  are  on  the  line  A  B,  parallel  to  CD, 
and  49  j^ards  from  it;  the  faces  A  K,  B  31,  are  138.81  yards, 
and  parallel  to  the  counterscarps  directed  on  D",  which 
form  the  gorge  walls  of  the  counterguards ;  the  flanks 
KL,  MN,  are  perpendicular  to  the  exterior  side,  and  are 
terminated  on  a  line  parallel  to  it  through  the  shoulder 
angles  of  the  bastions. 

487... An  elbow  cut,  5.46  yards  wide,  is  made  across  the 
counterguards  at  84.16  yards  from  the  salient;  the  portion, 
of  the  counterguard  behind  the  cut  is  arranged  for  cannon. 
The  ditches  of  the  counterguards  are  21.86  yards  wide  at 
the  salients;  the  counterscarps  are  directed  upon  a  point, 
0",  at  18.53  yards  from  O. 

488... A  casemated  caponniere  is  placed  in  advance  of  the 
counterguards,  the  middle  of  its  gorge  being  on  the  line, 
yli?,  joining  the  salients  of  the  counterguards,  and  its  sali- 
ent, P,  at  103.83  yards  from  C;  its  faces,  P,  U',  are  29.51 
yards  long,  and  directed  on  points  at  5.46  yards  from  the 
shoulder  angles,  K,  M,  of  the  counterguards ;  its  flanks, 
U',  V,  are  36.07  yards  long  and  perpendicular  to  the  exte- 
rior side. 

489. ..To  construct  the  demilune,  points  31",  M'"  are 
taken  on  the  bastion  faces  at  18.58  yards  from  the  shoulder 
angle,  and  on  the  line  joining  them  an  equilateral  triangle 
is  formed,  the  vertex  of  which,  H,  is  the  salient  of  the 
demilune,  and  the  two  sides  the  directions  of  the  faces, 
HS,  H  T,  which  are  164  yards  long.  An  elbow  cut,  5.46 
yards  wide,  is  made  on  each  face  at  109.3  yards  from  the 
salient  H,  and  separates  the  portion  ./from  the  salient. 

490. ..The  salient,  Q,  of  the  demilune  redoubt  is  55  yards 
from  the  salient,  P,  of  the  caponniere;  its  faces,  Q,  U,  are 
parallel  to  those  of  the  demilune,  and  65.58  yards  long. 


156  IIAXO'S    METHOD. 

The  flanks,  U  V,  X  Y,  ure  parallel  to  the  capital,  and  ter- 
niiyated  on  lines,  xx\  di-awn  IVoni  x  on  the  counterscarp  of 
the  redoubt  to  x'  on  the  line  A  B,  at  6.56  yards  from  the 
flanks  of  the  caponniere. 

41)1... The  counterscarps  of  the  counterguards,  from  the 
points  c",  e"\  on  the  prolonged  faces  of  the  demilune,  are 
directed  on  points  on  the  flanks  of  the  caponniere,  at  10.93 
yards  from  their  extremities,  to  points  /,  at  13.11  yards 
from  these  flanks ;  and  from  /  they  are  broken  parallel  to 
the  flanks,  and  continued  to  g  on  the  line  x  x'. 

492... A  casemated  redoubt  is  placed  in  each  re-entering 
place  of  arms;  its  face,  be,  is  directed  on  a  point,  c',  at 
36.07  yards  from  c",  and  is  39.35  \'ards  long;  the  other 
face,  hd,  is  perpendicular  to  be,  and  21.86  j-ards  long. 

493... A  casemated  redoubt  is  also  placed  in  the  salient 
place  of  arms  of  the  demilune  covered-way.  The  covered- 
way  and  the  re-entering  places  of  arms  are  arranged  in  the 
usual  manner  for  sorties,  and  with  traverses. 

494. ..Interior  retrenchments  are  arranged  in  the  bastions. 
In  the  one  on  tlie  right,  the  parapet  of  the  flank  is  broken 
to  increase  the  amount  of  flank  tire.  In  the  one  on  the  left, 
a  high  cavalier  is  placed,  having  one  tier  of  casemated  tire, 
with  earthen  embrasures  like  those  already  described,  and 
which,  from  their  having  been  introduced  by  Ilaxo,  are 
known  as  the  Ilaxo  casemate,  \\ith  an  ujiper  tier  of  uncov- 
ered tire. 

The  ditches  of  these  retrenchments  are  swept  from  the 
opposite  flanks. 

495... Ilaxo  casemates  are  placed  in  the  salients  of  the 
counterguards  and  the  salient  of  the  demilune. 

496.. .The  portions  of  the  curtain  parapet  of  the  enceinte, 
near  the  curtain  angle,  are  retired  to  give  a  more  eftective 
direction  to  the  guns  on  these  jiortions,  and  to  lengthen  the 
parapets  of  the  flanks. 

497... The  communication  from  the  enceinte  to  the  main 
ditch  is  by  a  postern  under  the  curtain.  The  communica- 
tions with  the  counterguards  and  other  outworks  are 
through  the  ditch,  between  the  flanks  of  the  enceinte  and 


IIAXO'S    METHOD.  157 

the  tenaille;  the  communication  in  front  of  the  tenaille 
being  covered  by  the  crest  l^  I  of  the  glacis  in  front  of  it, 
and  by  the  traverse  R^  and  tliat  across  the  main  ditch  to 
the  main  caponniere  by  the  double  caponniere  K'. 

498. ..The  ramps,  stairs  and  other  passages  leading  to  tlie 
terrepleins  of  the  difi'erent  works  are  indicated  on  the  plan, 
and  are  so  placed  as  to  satisfy  the  conditions  laid  down  for 
these  important  elements  of  a  front. 

490. ..The  plane  of  comparison  to  which  the  plan  is  refer- 
red is  taken  at  GO  feet  below  the  plane  of  site.  Tlic  relative 
command  and  the  relief  of  the  enceinte  and  other  compo- 
nent parts  are  thus  easily  deduced ;  and  it  will  be  seen  that 
everj'  advanced  part  is  well  swept  by  the  fire  of  the  more 
retired  parts. 

500... From  an  examination  of  the  plan,  it  will  be  further 
apparent  that,  by  the  position  and  length  given  to  the  faces 
and  flanks  of  the  bastions,  the  former  are  less  exposed  to 
enfilading  views,  and  the  fire  of  the  latter  is  considerably 
increased,  as  compared  with  Cormontaingne's  method  and 
the  subsequent  modifications  of  it ;  this  increase  in  the 
number  of  guns  that  maj'  be  brought  to  bear  on  the  posi- 
tions of  the  besieger  is  further  increased  by  the  flanks  of 
the  tenaille,  those  of  the  counterguards,  and  the  flanks  of 
the  cavalier. 

501... The  counterguards,  with  the  tenaille,  mask  com- 
pletely the  scarp  of  the  enceinte  from  any  position  that  the 
besieger's  batteries  can  occupy  beyond  the  main  ditch.  All 
the  outworks  exterior  to  the  counterguards  are  well  swept 
and  flanked  by  the  fire  of  the  latter, 

502. ..The  batteries  of  the  flanks  of  the  casemated  capon- 
niere sweep  effectively  every  point  in  advance  of  them,  and 
see  in  reverse  the  breaches  that  can  be  made  in  the  counter- 
guards.  The  scarp  of  this  work,  as  well  as  that  of  the 
counterguards,  is  masked  by  the  plan  and  relief  given  to 
the  counterscarp  of  the  main  ditch  and  the  covering  masses 
of  earth  behind  it,  from  the  besieger's  batteries  on  the  cresta 
of  the  bastion  and  demilune  salient  places  of  arms. 

503. ..The  demilune,  from  its  salient  position,  has  strong 


158  choumara's  method. 

reverse  views,  upon  the  glacis  in  advance  of  the  salients  of 
the  enceinte,  from  the  casemated,  battery  in  its  salient ; 
whilst  the  mass  of  this  batterj'  serves  as  a  traverse  to  cover 
the  portions  of  the  faces  in  rear  of  it  from  enfilading  fire. 
The  demilune  redoubt  serves  the  usual  purpose  of  this 
work ;  its  flank  is  casemated. 

504... Although  not  clearly  indicated  on  the  plan,  the 
parapets  of  those  portions  of  the  works  exposed  to  be 
breached  are  thrown  back  from  the  scarp  wall,  and  a 
chemin  de  ronde  is  formed  at  the  foot  of  the  parapet.  By 
this  disposition,  a  breach,  when  made,  will  be  more  difiicult 
of  assault ;  the  retired  position  of  the  parapet  will  be  less 
exposed  to  ricochet  fire,  and  the  chemin  de  ronde  will  afl:brd 
both  greater  security  from  surprise  and  a  good  position  for 
sharp-shooters  against  the  trenches. 

505... It  is  estimated  that,  by  allowing  the  usual  progress 
of  the  besieger's  approaches,  Haxo's  front  will  require  about 
50  days  for  its  reduction.  The  besiegers,  besides  the  ordi- 
nary trenches,  batteries  and  descents,  will  have  to  resort  to 
at  least  five  epochs  of  breaching  batteries:  1st,  for  opening 
the  demilune  and  the  redoubt  of  the  salient  place  of  arms; 
2d,  against  the  demilune  redoubt,  the  portion  of  the  demi- 
lune in  rear  of  the  cut,  and  the  redoubt  of  the  re-entering 
place  of  arms ;  3d,  against  the  counterguards  and  the 
casemated  caponniere;  4th,  against  the  bastion  faces;  and, 
5th,  against  the  interior  retrenchments. 


dlhoumara'.'i  pdlioil. 


506...Choumara,  a  French  ofiicer  of  engineers,  of  distin- 
guished abilities,  is  the  author  of  several  remarkable  me- 
moirs on  the  defects  of  the  bastioned  system,  and  the  means 
by  tv^hich  they  may  be  removed,  and  very  great  additional 


ciioumara's  method.  159 

strength  be  thereby  given  to  the  defences.    His  propositions 
for  this  purpose  may  be  briefly  stated  as  follows : 

507. ..1st.  That  part*  of  a  permanent  work  which  can 
undergo  no  modification  during  the  progress  of  a  siege  is 
the  masonry,  and  it  niay,  therefore,  be  regarded  as  the 
really  permanent  feature;  all  the  parts  of  earth,  as  the 
parapets,  etc.,  being  susceptible  of  such  modifications  as 
circumstances  may  demand. 

This  Choumara  terms  the  independence  of  the  parapets 
as  respects  the  scarps.  This  latter,  upon  whicli  the  security 
of  the  work  against  an  open  assault  or  a  surprise  depends, 
must  necessarily  receive  a  direction,  such  that  it  can  be 
swept  by  the  flanking  arrangements,  a  necessity  that  does 
not  exist  for  the  parapets,  which  may  receive  any  direction 
compatible  Avitli  the  interior  space. 

The  parapets  may,  therefore,  be  thrown  back  from  the 
salients,  as  in  the  bastion,  Pl.  19,  Fig.  1,  and  receive  a 
curvilinear  form  to  throw  a  greater  volume  of  fire  in  the 
direction  of  the  capital ;  or  they  can  be  retired  from  the 
faces,  as  in  the  bastion.  Fig.  A,  for  the  purpose  of  giving 
them  such  directions  that  their  prolongations  shall  cut  the 
adjacent  demilunes,  and  thus  be  masked  from  enfilading 
views ;  or  they  may  be  prolonged  so  as  to  afford  a  greater 
column  of  flank  fire,  as  in  the  flanks  /,  Fig  1 ;  or  they  may 
be  broken  into  any  direction  for  the  same  purpose,  or  to 
give  a  more  effective  direction  to  their  fire;  or,  finallj^  the}^ 
may  be  thrown  back  from  the  scarp  walls  instead  of  restino* 
immediatclv  upon  them,  and  thus  render  a  breach  less  prac- 
ticable, since  the  whole,  or  a  portion  of  the  parapet,  will 
still  retain  its  place  after  the  breach  has  been  made  in  the 
scarp — depending  on  the  distance  at  which  the  parapet  has 
been  moved  back.  In  all  of  these  cases  of  the  application 
of  the  independence  of  the  parapets,  Choumara  proposes  to 
convert  the  space  left  between  the  foot  of  the  parapet  and 
the  scarp  wall  into  a  chemin  de  ronde,  or  corridor,  which  is 
covered  in  front  by  a  slight  parapet,  and  from  enfilading 
fire,  by  a  bonnet  of  suitable  height  at  the  salients,  as  in  Figs. 
1,  A,  B,  etc.     This  corridor  is  occupied  by  sharp-shoCters, 


160  choumara's  method. 

to  annoy  the  besieger's  trenches.  Furthermore,  Chonmara 
regards  the  corridor  as  an  additional  security  against  sur- 
prise and  escalade. 

508... 2d.  Choumara  proposes  to  place  high  traverses  in 
the  bastion  salients,  to  cover  the  faces  from  enfilade,  and 
the  flanks  from  reverse  views;  and  similar  traverses  at  the 
shoulder  angles,  with  the  same  object.  These  he  also  pro- 
poses to  casemate,  or  else  construct  with  blindages  for 
artillery  to  obtain  afire  in  the  directions  of  the  capitals,  and 
reverse  views  on  the  demilune  glacis  and  the  breach  in  the 
bastion  face.  As  these  traverses,  from  their  height,  might 
give  the  besiegers  in  possession  of  them  a  plunging  fire  on 
the  bastion  retrenchments,  Choumara  proposes  so  to  arrange 
them  that  they  can  be  readily  destroj^ed  at  any  moment  by 
mines,  or,  if  of  timber,  be  burned. 

509. ..3d.  To  mask  the  masonry  of  the  enceinte  and  demi- 
lune from  breaching  batteries,  erected  in  their  usual  posi- 
tions along  the  crests  of  the  glacis,  Choumara  proposes  to 
form  what  he  terms  an  inierior  glacis,  or  covering  mass  of 
earth,  in  the  ditches,  the  crests  of  which  shall  mask  the 
masonry  of  the  scarps  from  the  positions  in  question ;  and 
the  upper  surface  of  which,  forming  a  glacis,  shall  be  swept 
by  the  fire  of  the  works  in  its  rear.  In  this  manner, 
Choumara  proposes  to  force  the  besiegers  to  the  ditficult 
operation  of  making  lodgments  in  this  glacis,  to  obtain 
suitable  positions  for  their  breaching  batteries. 

510. ..4th.  Choumara  proposes,  by  a  judicious  selection  of 
positions  for  some  of  the  outworks,  to  occupy  those  posi- 
tions on  the  exterior  which  are  most  favorable  to  the 
sharp-shooters  of  the  besiegers,  and  thus  cripple  this  im- 
portant arm  of  the  attack. 

511... 5th.  By  giving  greater  extent  to  the  exterior  side, 
and  a  more  retired  position  to  the  curtain,  which  is  also  to 
be  made  as  short  as  possible,  Choumara  proposes  to  obtain 
bastions  of  ample  size,  not  only  to  admit  of  the  modifica- 
tions he  proposes  for  the  parapets,  traverses  and  chemins  de 
ronde,  but  for  strong  interior  retrenchments,  so  organized 
with  bomb-proof  shelters,  and  arranged  defensively  toward 


choumara's  method.  161 

the  interior,  that  each  hastion  will  admit  of  a  defence  to 
the  rear  at  its  gorge,  after  the  besiegers  nia}'  have  effected 
a  breach  at  other  points,  and  penetrated  within  the  en- 
ceinte. 

512... Plan.  In  adapting  these  propositions  to  a  bastion- 
ed  front,  Chonniara  proposes,  in  order  to  obtain  the  requis- 
ite room  in  the  interior  of  the  bastions  and  a  lara:e  increase 
of  flank  fire,  to  take  the  exterior  side  from  400  to  600 
metres,  French.  In  the  front,  Fig.  1,  PI.  19,  for  example, 
the  exterior  side  is  440  metres;  the  lines  of  defence  are 
drawn  through  a  point  on  the  perpendicular  of  the  front  at 
74  ni.,  or  ^  of  440  m.  within  the  exterior  side  ;  the  faces  are 
150  m.,  and  the  flanks,  drawn  perpendicular  to  the  lines  of 
defence,  arc  85  m. — a  length  which  prolongs  them  35  m. 
within  their  intersections  with  the  lines  of  defence.  By 
this  construction,  the  curtain,  wliicli  will  be  115m.  long, 
will  be  well  swept,  and  the  gun  at  the  curtain  angle  can  be 
brought  to  bear  on  the  one  of  the  besieger's  counter-bat- 
tery against  the  flanks  which  are  furthest  out,  thus  frivino- 
a  very  great  preponderance  in  tire  to  the  flank  over  the 
counter-battery. 

513... The  deep  re-entering  thus  formed  between  the  flanks 
and  curtains,  gives  ample  room  for  a  tcnaille  with  flanks  ibr 
four  guns;  these  guns  are  covered  in  flank  by  a  traverse. 
The  tcnaille  is  not  revetted  in  front  of  its  curtain  and 
flanks,  or  at  its  gorge.  It  masks  sufticiently  the  scarp  of 
the  flanks  and  curtain  of  the  enceinte,  to  prevent  any 
danger  to  the  latter  from  the  destruction  of  the  portion  of 
the  scarp  wall  that  can  be  seen  over  the  tenaille. 

514... The  salient  of  the  demilune  is  the  vertex  of  an 
equilateral  triangle,  the  base  of  which  is  drawn  between 
two  })oints  on  the  bastion  faces,  at  18  m.  from  the  shoulder 
angles.  The  faces  of  the  demilune,  Z),  are  144  metres,  and 
revetted.  The  [>araj)et  of  the  demilune  is  thrown  back 
from  the  revetement,  leaving  a  corridor  covered  by  a  j)ara- 
pet  at  the  foot  of  its  exterior  slope.  The  parapet  is  broken 
near  the  gorge,  so  as  to  give  two  short  flanks  of  13  m.  per- 
pendicular to  the  exterior  side.  The  salient  is  occupied  bv 
11 


162  CnOUMAllA'S    METHOD. 

a  cascinatcd  traverse  with  flanks  for  tliree  guns.  This  trav- 
erse masks  the  interior  of  the  demihme  and  the  corridor 
from  enfilading  views.  A  disposition  is  shown  for  cuts 
across  the  demilune  faces,  the  parapets  of  which  are  to  be 
thrown  up  after  the  siege  commences.  The  demilune  ditch 
is  17  m.  wide.  The  portion  of  this  ditch  tow^ard  the  gorge 
slopes  upward  as  a  glacis,  and  is  swept  by  the  fire  of  the 
enceinte. 

515. ..The  interior  glacis  of  the  demilune  commences  at 
the  counterscarp  of  this  work,  and  has  a  glacis-slo[>e  out- 
ward, its  width  being  45  m.  Here  commences  the  revetted 
gorge  of  the  covered-w^ay.  The  width  of  the  covered-w^ay 
is  10  m.  Its  interior  crest  is  an  indented  line.  There  are 
no  traverses  in  this  work,  unless  required  for  its  defilement. 

51G...A  spacious  and  strong  redoubt  is  placed  in  the  demi- 
hme salient  place  of  arms.  Its  faces  are  13i!  m.  long,  and 
revetted.  Its  parapet  is  throwni  back,  leaving  a  corridor  in 
front  of  it,  and  is  curved  at  the  salient  for  five  guns,  sweep- 
ing along  the  capital.  A  bonnet  is  placed  in  its  salient  to 
cover  the  corridor  from  enfilade,  and  two  traverses  for  the 
same  object  on  its  terreplein.  This  redoubt  forms  a  mask 
for  the  portion  of  the  demilune  occupied  by  the  traverse. 

517...Choumara  places  strong  redoubts,  M,  with  revetted 
scarps  and  gorges  in  the  re-entering  place  of  arms.  The 
parapets  of  these  works  are  curved  at  the  salients  for  batte- 
ries to  sweep  the  approaches  on  the  bastion  capitals  and 
the  demilune  glacis,  and  they  are  thrown  back  from  the 
scarp  walls  to  give  a  corridor  for  sharp-shooters.  As  these 
redoubts  are  necessarily  contracted,  Choumara  prefers  to 
them  a  strong  redoubt  of  larger  dimensions,  placed  in  the 
bastion  salient  place  of  arms,  and  organized  like  the  pre- 
ceding. 

518... One  of  the  most  striking  features  of  Ohoumara's 
modifications,  is  the  mode  in  which  he  proposes  to  organ- 
ize the  large  bastions,  with  defences  which  shall  serve  as 
an  interior  retrenchment  in  case  the  bastion  is  one  of  the 
points  of  attack;  or  convert  the  bastion  into  an  isolated 
fort,  or  citadel,  for  the  garrison,  in  case  the  besieger  gains 


choumara's  method.  163 

possession  of  the  interior  of  the  enceinte  tiironoh  an  assault. 
This  he  proposes  to  aecomplisli  by  increasing  the  lengtlis 
of  the  exterior  side,  and  also  of  the  bastion  flanks. 

519...Witli  this  object,  Chouniara  places  a  row  of  case- 
mates within  the  bastions,  on  a  line  perpendicular  to  their 
capitals.     Each  casemate  is  from  60  to  SO  feet  long,  from 
12  to  20  feet  wide,  and  12  feet  high.    This  row  of  casemates 
serves  as  a  curtain  both  for  the  retrenchment  of  the  bastion 
and  for  the  defence  of  the  gorge  against  an  interior  attack. 
For  the  defence  of  the  salient  portion  of  the  bastion,  a  cut 
is  made  across  eacli  face  and  extended  to  the  cni)ital.     The 
scarp  of  this  cut  is  made  into  the  form  of  a  bastion  front 
with  orillons  at  the  shoulder  angles;  the  casemates  form- 
ing the  curtain  of  this  front.     The  counterscarp  of  the  cut 
may  be  either  revetted  or  have  a  simple  slope  of  earth.    In 
the  latter  case,  the  bottom  of  the  ditch  of  the  front  at  the 
foot  of  the  scarp  wall  is  at  a  suitable  level  to  adnut  of  a 
suitable  height  of  scarp  wall  to  secure  it  from  escalade.     A 
broad  ramp  leads  from  tlie  centre  casemate,  along  the  capi- 
tal toward  the  bastion  salient,  to  the  counterscarp  of  the  cut, 
and  there  branches  into  two  other  ranijis,  leading  up  to  the 
bastion  tcrre})Iein  on  the  right  and  left.    Until  the  besiegers 
are  al)out  to  breach  the  bastion  faces,  their  parapets  are  left 
intact,  and  the  [tortious  of  the  cut  along  which  the  ])ara- 
pcts  run  are  filled  up,  as  in  the  bastion  on  the  right,  thus 
leaving  a  free  communication  throughout  the   interior  of 
the  bastion.     So  soon  as  it  is  thought  necessary  to  cut  otf 
this  communication,  and  to  get  the  retrenched  portion  in  a 
state  of  defence,  that  portion  of  the  parapet  across  the  cuts 
is  demolished,  the  cut  excavated  and  suitably  arranged,  and 
the  parapet  of  the  reticnchnient  formed  in  part  of  the  eartli 
arising  IVom  these  changes.     The  jiarapet  of  the  front  of 
the  retrenchment   is  thrown   back,   leaving  a  corridor  for 
sharp-shooters  covered  by  a  slight  parapet;  that  portion  of 
this  corridor  along  the  I'ctired  flank  being  covered  by  tlie 
earthern  mask  of  the  orillon.     Chouniara  further  proposes, 
where  there  is  a  probability  of  the  scarp  of  the  bastion  face, 
which  closes  the  cut  on  the  exterior,  being  opened,  so  that 


164  choumara's  method. 

a  breach  might  be  made,  hj  firing  through  it,  on  the  flank 
of  the  retrenchment,  to  run  the  scarp  wall  of  the  retrench- 
ment at  right  angles  across  the  cut,  as  shown  on  the  right 
face  of  the  left  bastion,  and  to  arrange  the  bastionnet,  which 
this  modification  wonld  give  at  the  shoulder  angle,  for  sharp- 
shooters. 

520. ..To  expose  the  interior  of  the  retrenchment  to  the 
fire  of  the  flanks  of  the  adjacent  bastions,  and  to  the  para- 
pet of  a  second  retired  interior  retrenchment,  resting  on 
the  two  curtains  adjacent  to  the  bastion  of  attack,  a  portion 
of  the  parapet  of  the  bastion  flanks,  near  the  curtain,  is 
demolished,  and  a  slope  is  giveh  to  the  portion  of  the  ter- 
replein  on  which  it  rested.  The  retired  interior  retrench- 
ment Choumara  proposes  to  make  an  earthen-work  in  the 
form  of  a  bastioned  front,  breaking  the  faces  in  the  most 
suitable  manner  to  sweep  tlie  rear  of  the  retrenchment  in 
its  front. 

521... The  dispositions  to  convert  the  bastion  into  a  cita- 
del are  similar  to  the  preceding,  consisting  of  a  small  front, 
the  faces  of  whicli  are  nearly-  in  the  prolongations  of  the 
adjacent  curtains,  wnth  orillons  to  cover  the  corridor  of  the 
retired  flank.  This  front  has  a  covered-way  and  glacis  in 
advance  of  it,  the  crest  of  which  masks  the  scarp. 

522... Choumara  has  made  an  ample  provision  for  an 
easy  communication  between  all  points  of  the  enceinte  and 
the  outworks,  so  placing  them  as  to  be  well  covered  from 
the  besieger's  fire  and  well  swept  by  that  of  the  garrison — 
preferring  wide  ramps  for  this  purpose.  The  communica- 
tion from  the  enceinte  with  the  main  ditch  is  through  gate- 
ways in  the  scarp  wall  of  the  curtain,  at  its  extremities. 
The  rampart  at  these  points  is  removed  to  the  level  of  the 
main  ditch  ;  the  portion  of  it  between  them,  along  the 
centre  of  the  curtain,  being  sustained  at  the  ends  by  revete- 
ment  walls  run  back  perpendicularly  to  the  scarp  wall  of 
the  curtain.  Ramps  lead  from  the  gorges  of  the  bastions 
down  to  these  outlets  into  the  main  ditch.  From  these 
outlets  the  communications  to  the  outworks  are  around  the 
flanks  of  the  tenaille,  and  through  the  enceinte  ditch,  to 


cuoumaua's  method.  165 

riinips  placed  uloiig'  the  enceinte  counterscarp  leading  into 
the  demilune,  the  demilune  ditch,  the  enceinte  covered- 
way,  and  its  redoubts  in  the  places  of  arms ;  and  from  the 
demilune  ditch  to  the  redoubt  of  the  demilune  salient  place 
of  arms.  Posterns  on  the  faces  and  iianks  of  the  bastions, 
near  the  shoulder  angles,  lead  to  the  corridors  of  the 
enceinte.  Passages  are  left  at  the  ends  of  the  faces  of  the 
outworks,  leading  from  their  corridors  to  the  interior  of, 
the  W(^)rks.  To  keep  o[ten  the  communication  between  the 
bastions,  a  galler}'  between  their  gorges  is  made  along  the 
curtain  wall. 

528... For  the  security  of  tlie  casemates,  barricades  can 
be  nuide  in  their  doors  and  windows,  by  means  of  tim1)cr 
let  in  grooves  made  in  the  walls ;  the  space  between  the 
exterior  and  interior  timber  facing  being  tilled  with  sand- 
bags. 

524  ...Remarks.  The  memoirs  in  wliich  Choumara 
brought  his  propositions  before  the  public  naturally  at- 
tracted attention,  as  much,  perhaps,  from  their  }>olemical 
character  and  piquancy  of  style  as  their  professional  inter- 
est. They  contain  but  few  things,  the  germs  of  which  are 
not  to  be  found  in  writers  who  preceded  him.  His  modi- 
fications respecting  the  parapets,  throwing  them  back  from 
the  scarps  and  breaking  them  into  directions  best  suited 
for  defence,  are  to  be  met  with  in  Chasseloups  pro[)ositions. 
His  proposals  for  lengthening  the  bastion  flanks,  and  occu- 
pying the  salient  places  of  arms  by  redoubts  with  consid- 
erable command,  are  to  be  found  in  the  method  of  cfc  la 
Chiche.  To  Virgin  he  seems  to  be  indebted  for  liis  organi- 
zation of  interior  retrenchments,  which  are  to  convert  each 
bastion  into  an  indejiendent  work,  equally  provided  for 
defence  against  approaches,  both  from  the  interior  and 
exterior  of  the  enceinte.  Like  disputants,  usually  of  an 
ardent  temperament,  he  over  estimates  the  value  of  many 
of  his  propositions,  and  loses  sight  of  their  countervailing 
defects.  By  laying  down  as  a  principle  what  may  be  ex- 
ceptionably  good  in  practice,  he  has  rather  weakened  his 
own  positions.     This  is  the  case,  particularly,  with  his  rule 


166  cnorjiARA's  method. 

of  the  independence  of  the  parapets  on  the  scarps,  whicl), 
if  adopted  in  all  cases,  might  demand  a  greatly  increased 
and  hurtfnl  command,  and  cut  up  to  great  disadvantage 
the  interior  spaces  of  the  bastions.  His  introduction  of 
the  ehemins  de  ronde  on  the  faces  of  the  bastion  and  demi- 
lune, add  reallj  very  little,  if  at  all,  to  the  exterior  defence; 
whilst  they  contract  the  interior  space  of  these  works, 
break  in  upon  the  unity  of  the  defence,  and  place  the  troops 
in  them  in  a  very  exposed  position  to  the  means  of  annoy- 
ance possessed  by  the  besieger.  His  expectations  with 
respect  to  the  effect  of  his  tire  in  the  direction  of  the  capi- 
tals, in  delaying  the  besieger's  approaches  up  to  the  third 
parallel,  were  hardly  warranted  by  the  experience  gained 
in  artillery  and  small  arms,  even  at  the  time  the  last  edition 
of  his  memoirs  appeared.  It  is  hardly  to  be  questioned, 
now  that  these  weapons  have  been  so  greatly  improved, 
both  in  range  and  accuracy  of  fire,  that,  considering  the 
increased  development  of  the  besieger's  parallels,  which 
gives  him  a  choice  of  positions  for  his  batteries  on  so  ex- 
tended a  line,  the  concentrated  iire  he  could  bring  to  bear 
on  the  batteries  in  question  would  not  only  soon  ruin  their 
casemates,  but  would  greatly  damage  the  adjacent  faces, 
and  also  the  flaidvs  of  the  bastions,  although  covered  from 
enfilading  views,  either  by  the  direction  of  the  parapets  of 
the  fiices  or  the  high  traverses  raised  with  the  same  object. 
These  advantages  in  the  position  of  the  besieger,  it  is 
thought,  would  prevent  any  delay  in  pushing  forward  his 
approaches  up  to  the  third  parallel.  After  this,  the  ap- 
proaches would  probably  be  retarded  beyond  the  usual 
time  allowed  in  the  attack  on  Cormontaingne's  front,  owing 
chiefly  to  the  redoubts  in  the  bastion  and  demilune  salient 
places  of  arms  and  the  arrangement  of  the  face-cover  in 
the  enceinte  ditch. 

525... Supposing  an  enceinte  organized  according  to  his 
method,  and  containing  interior  retrenchments  to  oppose 
the  besieger's  approaches,  both  from  without  and  within 
the  enceinte,  Choumara  estimates  at  least  six  separate 
epochs  of  breaching  batteries,  as  follows  :  1st,  against  the 


coehorn's  method.  1G7 

redoubt  of  the  dcmihine  salient  place  of  arms;  2d,  against 
the  demilune  and  the  redoubt  of  the  bastion  salient  places 
of  arms;  3d,  against  the  bastions ;  4th,  against  the  l)astion 
retrenchment;  5th,  against  the  retired  retrenchment;  6th, 
and  finally,  against  the  bastions  converted  into  citadels  by 
the  fronts  witli  wliich  their  tjorijes  are  closed.  Accordins: 
to  the  estimate  of  time  made  by  Chouniara,  it  would  re- 
quire 112  days  from  the  opening  of  the  trendies  to  the  final 
assault  and  reduction  of  the  last  defences. 


Olocliorii'.'j  Mietliod. 


526...Coehorn,  a  Dutch  engineer  of  great  eminence,  was 
the  contemporary  and  rival  of  Vauban,  both  in  actual  war- 
fare and  in  the  engineer's  art.  Like  Yauban,  he  is  the 
author  of  sevei-al  methods,  in  which  he  has  sliown  tlie  same 
pre-eminent  skill  as  Vauban,  in  the  adajitation  of  his  art  to 
h)cal  features,  and,  [»crlia[is,  moi'c  originality  in  liis  combi- 
nations ;  for  Vauban  rather  made  use  of,  and  improved 
upon,  the  defensive  branch  of  his  art,  as  he  found  it,  than 
originated;  whereas,  many  of  Coehorn's  devices  are  liis 
own. 

527 ...  Coehorn's  fronts  arc  arranged  with  a  view  to 
aquatic  sites,  like  those  of  Holland,  where  water  is  found 
by  excavating  to  the  depth  of  a  few  feet  below  the  natural 
surface,  by  means  of  which,  wet  ditclies  can  be  combine<l 
with  those  which  are  dry,  so  as  to  procure  not  only  secur- 
ity against  a  surprise,  but,  as  will  be  seen  further  on,  to 
aftbrd  facilities  for  an  active  defence  ajrainst  the  enemv 
when  in  [)OSsession  of  the  dry  ditches. 

528. ..Plan.  Coeliorn  luis  adopted  the  mode  of  laying 
out  the  lines  of  his  front,  used  by  some  of  the  earlier  en- 
gineers ;  fixing,  in  the  first  place,  the  interior  fiidcs  of  the 


168  coehorn's  method. 

space  to  be  enclosed,  taking  these  lines  as  tlie  magistrals 
or  exterior  lines  of  the  curtains  in  the  bastioned  system. 

529. ..Assuming  A  B,  PI.  15,  as  the  position  of  the  inte- 
rior side,  Coehorn  makes  its  half  length,  A  B,  75  toises, 
French  measure.  From  A,  the  same  distance,  75  toises, 
being  set  off  to  Q  on  the  capital,  or  bisecting  line  of  the 
angle  of  the  polygon,  gives  the  salient  of  the  exterior  side; 
this  side  in  the  hexagon  being  224  toises.  Bisecting  A  B, 
the  half,  B  D,  is  taken  for  half  the  curtain. 

The  lines  of  defence  are  drawn  from  the  extreniities  of 
the  curtain,  thus  determined,  to  the  opposite  salients  of  the 
exterior  side.  From  the  salients  of  the  exterior  side,  as 
centres,  Mnth  the  lines  of  defence  as  radii,  arcs,  I)  6r,  being 
described,  give  the  faces,  C  G,  of  the  bastions  measured 
along  the  lines  of  defence. 

The  portions  of  the  faces  thus  determined  are  not  revet- 
ted toAvard  the  ditch  ;  the  exterior  slopes  of  their  parapets 
descending  below  the  water  level  to  the  bottom  of  the 
ditch,  as  shown  on  the  cross  section  G'  H'. 

530. ..At  the  shoulder  angle  of  the  bastion,  Coehorn  has 
placed  a  stone  tower,  of  which  G  I L  K H  is  the  plan. 

An  interior  elevation  of  this  tower  is  shown  on  the  sec- 
tion Q  R.  This  tower  is  arranged  on  top  with  a  parapet 
for  an  open  defence.  It  is  arranged  with  bomb-proof 
arches,  and  is  casemated  on  the  interior  side,  G  H,  to 
sweep  the  dr}'  ditch  between  the  bastion  and  the  cavalier 
Avithin  it. 

To  set  out  the  tower,  G  JI  \s  drawn  perpendicular  to 
G  C,  and  18  toises  in  length  ;  a  distance,  G  I,  of  8 J  toises 
is  taken  on  the  prolongation  of  C  G;  HK\q  drawn  paral- 
lel to  G  /,  and  4  toises  in  length  ;  ^  jL  is  found  by  joining 
K  with  the  opposite  salient,  making  K L  equal  to  14  toises 
taken  along  this  line  ;  the  points,  /and  L,  thus  determined, 
are  joined  by  an  arc  of  60°. 

The  curved  projecting  portion  of  the  tower  forms  an 
orillon,  which  covers  the  concave  ilank  P D,  which  is  also 
an  arc  of  00°. 

531... The  faces  and  flanks  of  the  cavalier  have  a  revetted 


coehorn's  method.  169 

scarp,  as  well  as  tbe  portion  D  S  of  the  curtain,  -which  is 
thrown  back  on  the  prolongation  of  the  line  of  defence, 
and  closes  the  gorge  of  the  bastion.  The  magistral  of  the 
face  of  the  cavalier  is  parallel  to  C  G\  and  22|  toises  from 
it.  The  magistral,  0  S,  of  the  flank  is  concentric  with  the 
one,  PI),  of  the  bastion,  a  ditch  16  toises  wide  being  left 
between  the  two  flanks. 

532. ..The  interior  of  bastion  face  (7(7,  which  forms  the 
counterscarp  of  the  cavalier,  is  arranged  with  a  loop-holed 
gallery  for  sweeping  the  cavalier  ditch. 

533. ..The  space  between  the  orillons  and  curtain  is  occu- 
pied bv  a  tenaiile,  of  which  /  U  T  V  xa  the  exterior  line  at 
the  water  level.  The  point  T  is  on  the  line  of  defence, 
and  at  140  toises  from  the  salient;  the  portion  T  U'ls  per- 
pendicular to  this  line  of  defence,  and  the  portions  /  f/and 
T  Fare  on  the  lines  of  defence. 

534. ..The  enceinte  ditch  is  24  toises  wide  at  the  water 
level.  An  earthen  counterguard,  D'  C.  for  musketry  de- 
fence is  placed  in  front  of  the  bastion. 

535. ..The  salient,  Z,  of  the  demilune  is  at  03  toises  from 
the  point  W^  where  the  enceinte  counterscarp  cuts  the 
capital  of  the  front;  its  demigorge,  TV X',  is  53 J  toises.  The 
demilune  ditch  is  18  toises  wide,  and  that  of  the  counter- 
guard  is  14  toises. 

536. ..The  demilune  contains  a  small  redoubt,  the  faces  of 
which  are  revetted,  and  parallel  to  those  of  the  demilune. 
The  ditch  of  the  redoubt  is  dry,  and  16  toises  wide.  A 
curvilinear  space  is  formed  at  the  gorge  of  the  redoubt,  to 
afl'ord  a  covei-ed  harl)()r  for  boats  used  for  communication. 
A  small  caponniere,  in  the  form  of  a  lunette,  is  placed  at 
the  gorge  of  the  redoubt  to  secure  the  retreat  of  the  troops 
from  it  to  the  boats.  The  walls  of  this  caponniere  are 
pierced  with  tAvo  tiers  of  loop-holes  ;  the  work  being  di- 
vided into  two  stories,  the  lower  being  covered  with  heavy 
beams  and  earth  to  resist  shells,  the  upper  being  uncovered. 

537.. .A  similarly  covered  caponniere,  of  a  rectangular 
shape,  for  one  tier  of  Arc,  is  placed  across  the  ditch  of  the 
redoubt,  near  its  extremity.    A  snudl  wet  ditch  is  })laced  iu 


170  coeiiorn's  method. 

front  of  this  work,  and  is  flanked  by  a  counterscarp  gallery 
under  tlie  portion  of  the  demilune  face  opposite  to  it. 

538. ..A  like  construction,  of  a  pentagonal  form,  is  placed 
within  the  salient  angle  of  the  demilune,  the  faces  of  which, 
toward  the  interior  of  this  work,  are  loop-holed  to  sweep 
the  ditch  of  the  redoubt  and  the  interior  of  the  demilune. 

539... The  covered-wa^^s  of  the  counterguard  and  demi- 
lune are  13  toises  wide;  a  re-entering  place  of  arms  is 
formed  at  the  junction  of  the  two,  the  faces  of  which  are 
30  toises. 

540... A  redoubt  of  a  quadrangular  shape,  the  faces  of 
which  are  respectively  12  and  15  toises,  and  which  is  a 
simple  loop-holed  wall,  closes,  in  connection  with  two 
traverses,  the  gorge  of  the  re-entering  place  of  arms. 

541... A  gallery,  covered  with  heavy  timber  and  earth, 
is  placed  6  toises  in  advance  of  the  re-entering  place  of 
arms,  to  furnish  a  tire  of  musketry  to  sweep  the  glacis  in 
front. 

One  of  the  most  prominent  features  in  Coehorn's  method 
is  the  combination  of  wet  and  dry  ditches,  with  a  view  to 
security  from  surprise,  and  for  protracting  the  defence  and 
disputing  the  possession  of  every  point  foot  by  foot.  For 
these  purposes  the  wet  ditches  are  made  very  wide  and 
contain  water,  at  least  six  feet  in  depth,  thus  forcing  the 
enemy  to  the  construction  of  long  dikes  to  efl:"ect  their 
passage;  whilst  the  bottom  of  the  dry  ditches  are  kept 
slightly  above  the  general  water  level,  so  as  to  compel  the 
enemy  to  bring  the  earth,  as  well  as  the  other  materials 
requisite  for  their  passage,  from  other  points.  In  addition 
to  these  purely  passive  means,  the  dry  ditches  are  organized 
for  an  active  defence  by  sorties,  and  are  well  swept  bv 
direct  and  reverse  fires  from  casemates,  counterscarp  gal- 
leries and  capounieres.  The  portion  of  the  dry  ditch 
between  the  faces  of  the  cavalier  and  bastion  is  swept  by 
artillery  in  the  casemates  under  the  orillon,  and  by  two 
pieces  behind  a  wall  pierced  with  embrasures,  which  closes 
the  space  between  the  shoulder  angle,  0,  of  the  cavalier, 
and  the  extremitv,  H  K,  of  the  orillon.     In  like  manner, 


coeiiorn's  method.  171 

the  ditch  between  the  flanks  is  swept  from  casemates  under 
t]je  portion  SD  of  the  curtain.  A  reverse  tire  of  mus- 
ketry sweeps  tlie  ditch  aUmg  tlie  face,  from  counterscarp 
galleries  under  the  bastion  faces,  and  from  a  gallery  along 
the  capital,  which  serves  as  a  communication  between  these 
galleries  and  the  interior. 

To  cut  oft"  the  communication  between  the  ditch  of  the 
face  and  flank,  a  wet  ditch  is  made  in  front  of  the  orillon 
and  the  connecting  wall.  This  ditch  is  flanked  by  the 
counterscarp  gallery.  Two  drawbridges  over  this  ditch 
form  a  means  for  sorties  on  the  enemy  whilst  ettecting  the 
passage  of  the  ditch  of  the  face.  A  drawbridge  for  a  like 
purpose  is  thrown  over  the  wet  ditch,  in  front  of  the 
caponniere  in  the  ditch  of  tbe  demilune  redoubt.  Besides 
these  provisions  for  carrying  on  what  the  French  well 
cx[)ress  by  loic  fjucrrc  dc  chicane^  Coehorn  nnikes  a  profuse 
use  of  palisadings  in  all  parts  of  his  iront  where  an  obsti- 
nate stand  is  to  be  made,  besides  employing  countermines 
to  destroy  such  parts  as,  being  in  the  enemy's  possession, 
would  be  prejudicial  to  the  defence. 

542. ..The  question  may  very  naturally  be  here  asked, 
to  what  extent  such  means  of  defence  may  be  depended 
upon?  The  answer  is,  only  so  far  as  they  can  be  ke})t  in  a 
good  condition  for  the  moment  when  they  can  be  brougbt 
into  play.  AVitli  the  ])rosent  improved  practice  of  artillery 
there  is  little  doubt  but  that  all  of  these  means  for  the  ditch 
defences,  as  provided  by  (^oehorn,  except  the  counterscar}) 
galleries,  would  be  destroyed  b}'  the  ricochet  Are  of  the 
enemy's  entilading  batteries  at  an  early  period  of  the  siege, 
the  masonry  of  the  loop-holed  redoubts  and  caponnieres 
being  altogether  too  slight  to  withstand  the  effects  of  this 
fire.  Could  these  means  be  kept  in  a  good  condition,  we 
have  tlie  wan-ant  of  numerous  sieges  in  favor  of  their  efli- 
cacy  in  the  hands  of  an  intelligent  and  resolute  garrison. 

543...rR0Fii-ES.  In  the  plan  and  profiles  the  horizontal 
plane  of  site  is  assumed  at  24  feet  above  the  plane  ol  com- 
jtarison.  From  an  examination  of  the  references  on  the 
figures  of  the  plate,  the  relief  and  relative  command  of  all 


172  coehorn's  method. 

the  works  are  readily  deduced.  It  will  be  seen,  on  exam- 
ining the  plan,  that  a  portion  of  the  bastion  face,  adjoining 
the  salient,  is  raised  3  feet  higher  than  the  portion  toward 
the  orillon,  thus  forming  a  bonnetfe,  which  not  only  gives  a 
greater  command  to  this  portion,  but  masks  more  etfectually 
the  ditch  and  masonry  of  the  cavalier.  A  like  arrangement 
is  seen  in  the  demihine  face,  both  at  the  salient  and  toward 
the  gorge,  and  with  a  like  view  to  mask  the  caponniere  and 
the  loop-holed  redoubt  in  the  salient  of  the  demilune. 

544...  Rem  ARKS.  It  will  be  seen,  on  reference  to  the  plan 
and  sections,  that  Coehorn  has  given  but  a  slight  command 
to  all  his  works — his  object  in  this  being  econoni}-,  and  to 
depend  rather  upon  the  near  than  the  distant  defence,  his 
dispositions  having  been  made  almost  exclusively  for  the 
formei".  The  command  of  the  crest  of  the  covered -way  is 
only  4|  feet  over  the  natui-al  site,  the  terreplein  of  this 
work,  whicli  is  7|  feet  below  the  crest,  being  thus  placed  a 
little  above  the  water  level,  with  a  view  to  compel  the  be- 
siegers to  bring  the  earth  and  materiel  from  a  distance  to 
form  a  cover  for  his  approaches  in  the  covered-way. 

545. ..The  only  dispositions  for  the  distant  defence  b}^  ar- 
tillery are  in  the  cavalier  and  demilune  redoubt,  except  in 
the  dry  ditches,  where  guns  and  mortars  might  be  placed  to 
fire  over  the  low  parapets  of  the  exterior  works. 

546... Besides  the  exposure  to  ricochet  caused  by  this 
slight  command,  the  directions  given  to  all  the  faces  of  the 
works  are  very  favorable  to  the  enemy's  entilading  batte- 
ries. 

547.. .The  dimensions  of  the  parapet  of  the  counterguard, 
which  serves  as  a  mask  for  the  tri})le  Hank  lire  of  the  cava- 
lier, bastion  and  tenaille,  and  those  of  the  parapets  of  the 
bastion  and  demilune,  which  serve  as  face  covers  for  the 
cavalier  and  demilune  redoubt,  are  insufKcient  for  these 
purposes,  as  they  could  readily  be  opened  by  shells  fired 
horizontally  into  them,  or  by  small  mines,  and  expose  the 
scarp  of  the  interior  works  to  the  enemy's  breach  batteries 
on  the  glacis.  The  scar})  walls,  moreover,  of  the  works  in 
q-uestion,  are  not  of  sufficient  height  to  secure  them  from 


TENAILLED    SYSTEM.  173 

an  open  assault.  Tlie  only  feature,  then,  of  the  ingenious 
eombiiiations  of  this  celebrated  engineer,  which  wouUl  find 
an  application  in  the  present  state  of  the  art,  is  the  combi- 
nation of  wet  and  dry  ditches  for  sites  similar  to  those  for 
which  his  dispositions  were  designed. 


©enaillcd  Sijfjtem, 


C^'lL^ 


548. ..Several  engineers,  of  professional  eminence,  have 
proposed  tenailled  enceintes,  as  offering  defensive  proper- 
ties superior  to  bastioned  enceintes.  This  system  has  found 
but  few  advocates;  and,  except  in  particular  localities, 
where  the  natural  features  of  the  site  demanded  it,  and  for 
small  works,  it  has  met  with  no  practical  applications. 

.541). ..Requiring  that  the  salient  angles  shall  not  be  less 
than  60°,  and  the  re-entering  angles  between  90°  and  100°, 
the  tenailled  system  is  oidy  adajjted  to  regular  polygons  of 
a  sufficient  number  of  sides  to  admit  of  these  conditions 
being  satisfied.  If  the  exterior  sides  are  kept  within  the 
limits  usually  admitted  by  engineers  for  bastioned  en- 
ceintes, the  faces  of  the  tenailles  become  very  long  and  the 
re-enterings  very  dee});  thus  presenting  two  serious  defects: 
long  lines  which  are  very  much  exposed  to  enfilade,  and  a 
great  diminution  of  the  interior  space  as  compared  with 
the  bastioned  enceinte.  The  ditches  when  dry  can  only  be 
swept  by  casemated  defences  in  the  re-entering  angles;  and 
even  then  but  partially,  unless  the  casemate  embrasures  are 
placed  very  near  the  level  of  the  bottom  of  the  ditch,  in 
which  case  the  enceinte  would  be  exposed  to  a  surprise 
through  the  embrasures;  and,  in  the  contrary  case,  liable 
to  a  like  attempt  from  the  dead  .space  at  the  re-enterings 
below  the  embrasures.  In  wet  ditches  this  exposure  to  sur- 
prise would  be  much  less  if  the  ditches  could  not  be  forded. 
In  either  case  the  defect  arising  from  embrasure  casemates 


174  carnot's  tenailled  method. 

placed  in  a  re-entering  angle,  would  be  a  serious  objection 
to  using  the  guns  of  e?cli  side  simultaneously.  When  the 
salient  angles  of  the  tenailles  are  acute,  the  effect  of  the  en- 
filading fire  would  not  be  felt  alone  on  the  face  enfiladed, 
but  upon  the  adjacent  face  in  front,  and  shot  passing  over 
would  damage  the  adjacent  tenailles. 

The  foregoing  are  the  chief  objections  to  this  system.  It 
presents  no  advantage  but  the  ver)'  illusory  one,  consider- 
ing the  consecjuences  arising  from  it,  of  long  faces  present- 
ino'  a  mutual  Hankino-  and  cross  fire  of  considerable  extent. 


iarnot's  ieniitllcd  Method. 


550... The  great  reputation  acquired  by  Carnot  during  the 
French  revolution,  in  "which  he  played  so  conspicuous  a 
part  as  a  soldier,  statesman  and  executive  officer,  connected 
with  his  professional  education  as  an  engineer  officer,  gave 
for  a  time  a  certain  prestige  to  his  views  on  fortification, 
which  caused  them  to  be  adopted  in  Germany,  where  they 
have  been  a[)plied  in  some  of  the  works  constructed  since 
1815. 

551... Struck  with  the  exposed  state  of  the  artillery,  on 
ramparts  without  bomb-proof  shelters,  to  ricochet  fires,  and 
the  feeble  resistance  offered  by  garrisons  in  some  of  the 
sieges  of  his  day,  particularly  in  an  active  defence  by  sor- 
ties, Carnot  seems  to  have  considered  the  Aveakness  attri- 
buted to  existing  fortifications  to  the  want  of  such  shelters, 
and  also  of  such  means  of  communication  with  the  exte- 
rior which  would  enable  the  garrison  to  sally  out  in  force 
and  assail  the  trenches  of  the  besiegers. 

552. ..The  systems  of  defence  which  he  has  proposed  are 
devised  to  remedy  these  two  prominent  defects,  and  consist 
in  providing  a  number  of  casemates,  on  suitable  points  of 


carnot's  tenatlled  method.  175 

the  defeneevS,  from  wliieli  a  constant  sliower  of  small  pro- 
jectiles and  hollow  shot  can  be  brouii^ht  u})on  the  besieger's 
works  ;  and,  instead  of  the  revetted  counterscar}),  Avhich 
constitutes  one  of  the  main  secnrities  ag-ainst  a  surprise — 
but  as  ordinarily  arranged  is  an  obstacle  in  the  Avaj  of 
throwing  rapidly  forward  a  considerable  body  of  troops 
from  the  interior  to  operate  on  the  exterior — he  proposes  to 
Ibrm  an  earthen  one  with  so  slight  a  slope  that  troops  can 
ascend  it  with  ease  to  make  sorties ;  the  ordinary  covered- 
way  and  ghicis  being  also  done  away  with  to  facilitate  these 
operations. 

5r);]...Carnot,  in  his  published  works,  has  given  his  views 
U[)()n  the  ameliorations  of  which  the  fortifications  of  his 
time  were  susceptible,  besides  some  new  combinations  for 
a  bastioned  system  and  two  tenailled  systems  for  acpiatic 
and  irregular  sites,  in  which  the  defects  of  this  latter  s^'S- 
tem  are  less  objectionable,  and  to  which  they  can  be  more 
easily  applied. 

554. ..Plan.  This  consists  of  a  continuous  enceinte,  PI. 
16,  Fig.  2,  formed  of  tenailles,  the  re-entering  angles  of 
which  are  90°,  and  the  salient  angles  not  less  than  60°. 
The  interior  of  the  place  is  enclosed  by  a  Avail,  vl,  of  suffi- 
cient height  to  be  secure  from  escalade  ;  the  [)lan  of  it  is  a 
tenailled  line,  with  re-entering  angles  of  'J0°  and  salients  of 
60°;  it  is  arranged  witli  two  tiers  of  loop-holes  for  mus- 
ketry, which  are  within  arched  recesses  in  the  wall,  of  suf- 
ticient  depth  to  screen  tlie  men  serving  them  from  vertical 
lire.  Casemated  batteries,  Q^  for  artillery,  are  jdaced  at 
the  re-enterings,  to  flank  the  ditch  between  the  wall  and 
the  eartlien  rampart  of  the  enceinte.  Tliis  wall  serves 
the  same  end  as  the  one  in  Montalembert's  method.  The 
salients,  A  A,  arc  about  250  yards  apart. 

555. ..The  rampart  and  parapet  of  the  body  of  the  place, 
(*,  are  detached  from  the  scarj)  wall  in  front,  a  narrow  cor- 
ridor being  left  between  the  foot  of  the  exterior  slo[)e  and 
the  back  of  the  wall.  The  wall  is  arranged  like  the  inte- 
rior one,  with  one  tier  only  of  loop-holes  for  musketry  Are. 
At  its  re-entering  it  is  broken  forward  and  is  pierced  with 


176  carnot's  tenailled  method. 

embrasures,  to  form  a  position,  Tr,  for  cannon  to  flank  the 
ditch  between  it  and  the  tenaille. 

556. ..The  tenaille,  6r,  masks  the  greater  portion  of  the 
scarp  of  the  body  of  the  place,  its  wings  being  about  120 
yards  in  length  ;  it  is  closed  by  a  detached  wall  with  loop- 
holes. 

557... From  the  re-entering  of  the  tenaille  a  double  capon- 
iiiere  of  earth  leads  by  a  ramp  to  an  earthen  redoubt,  jfiT, 
placed  at  the  re-entering  formed  by  the  counterscarps. 
This  redoubt  is  intended  to  hold  troops  in  readiness  for 
sorties,  and  is  without  a  ditch,  so  that  they  can  move  out 
over  its  parapet. 

558. ..Earthen  countei'guards,  the  salients  of  which,  B  B^ 
are  about  390  yards  apart,  mask  the  walls  of  the  body  of 
the  place  and  the  tenaille ;  sufficient  space  only  being  left 
between  their  extremities,  F,  F,  and  the  caponniere  for  the 
circulation  through  the  ditches.  This  work,  like  the  te- 
naille, has  a  narrow  terreplein,  and  is  intended  only  for  a 
defence  of  musketry,  except  at  the  salient  portions,  which, 
like  the  salients  of  the  enceinte,  are  arranged  for  artillery 
to  fire  in  the  direction  of  their  capitals  from  behind  blind- 
ages or  casemated  traverses. 

The  foot  of  the  parapet,  31  M,  of  the  redoubt  is  placed 
40  yards  within  the  line  joining  B  B. 

559... Profile.  The  positions  of  the  different  lines  on 
the  plan  are  readily  ascertained  from  the  section  on  J  K, 
Fig.  2,  as  the  lines  are  all  parallel.  The  relief  and  the 
relative  command  of  the  ditferent  parts  are  also  given  on 
the  same  section. 

560... Remarks.  The  expectations  of  Carnot  with  respect 
to  the  efficacy  of  the  proposed  shower  of  small  projectiles 
upon  the  trenches  of  the  besiegers,  from  the  casemates  for 
mortars  and  howitzers,  have  been  shown  from  experiments 
as  not  likely  to  be  realized.  From  similar  experiments,  the 
detached  scarp  walls  proposed  by  him  would  soon  be  over- 
thrown by  a  heavy  curvated  fire,  which  might  be  brought 
to  bear  upon  them  over  their  earthen  masks.  The  ditches 
and  terrepleins  of  all  the  parts  of  his  tenailled  method  are 


POLYGONAL    SYSTEM.  177 

peculiarly  exposed  to  ricocliet  fire,  whilst  the  long  wings  of 
the  tenaille  and  the  double  caponniere  mask,  to  a  great 
degree,  the  fire  of  the  enceinte  along  the  ditches.  The 
provision  made  for  sorties  from  the  redoubt  at  the  re-enter- 
ing of  the  earthen  inclined  counterscarps  is  exceedino-]y 
feeble,  and  it  is  not  easy  to  see  what  would  prevent  an 
active  enemy,  on  the  repulse  of  a  sortie,  from  following 
the  retreating  troops  into  the  works  themselves,  or,  having 
driven  them  into  the  ditches,  from  regaining  their  trenches 
with  comparatively  little  loss. 


ngonal  ^ptcni 


561... The  polygonal  system  has  been  proposed  by  several 
engineers  of  distinction,  but  its  most  ardent  advocate  has 
been  the  celebrated  Montalembert,  whose  views  have  been, 
more  or  less,  carried  out  in  many  of  the  more  recent  con- 
structions of  the  engineers  of  Germany. 

Consisting  of  either  a  simple  polygonal  enceinte  without 
re-enterings,  the  sides  of  which  are  flanked  by  casemated 
caponni^res,  placed  at  the  middle  point  of  the  fronts;  or  of 
fronts  either  slightly  tenailled,  or  of  a  bastioned  form,  with 
short  casemated  flanks  to  flank  the  faces  of  the  centra] 
capon nicres,  this  system  affords  more  interior  space,  and, 
from  the  mode  adopted  for  flanking  the  enceinte,  will  admit 
of  much  larger  fronts  than  either'the  bastioned  or  the  te- 
nailled systems.  The  salient  angles,  moreover,  will  be  more 
open  in  this  than  in  the  other  two  systems.  From  these 
peculiarities  of  this  system,  the  positions  suitable  for  the 
erection  of  batteries  to  enfilade  the  flices  of  the  enceinte 
are  less  advantageous,  from  their  being  thrown  in  nearer  to 
the  adjacent  fronts,  than  in  either  of  the  other  systems; 
whilst  a  greater  development  of  trenches  will  also  be 
12 


178  montalembert's  polygonal  method. 

reqnii^itG  to  envelop  tlie  fronts  of  attack.  Tliese  obvious 
advantages,  liowever,  are  more  than  counter))alance(]  by  tlio 
Avant  of  the  concentrated  cross  tires  whicli  are  aftbrded,  in 
both  the  bastioned  and  tenailled  s^'stems,  in  advance  of  the 
salients  of  the  enceinte,  and  upon  the  ground  generally  in 
advance  of  the  fronts.  Each  front  of  the  pol3-gonal  system 
offers,  moreover,  a  long  and  vulnerable  line  to  enfilading 
and  slant  fire,  which  will  also,  to  sou^e  extent,  take  eflect 
on  the  reverse  of  the  adjacent  fronts.  But  the  chief 
objection  to  this  system  lies  in  the  mode  adopted  for  flank- 
ing the  enceinte.  The  casemated  caponnieres  for  this 
pur[)Ose  being  exterior  to  the  enceinte,  it  will  be  exposed  to 
escalade  as  soon  as  the  fire  of  the  caponnieres  is  silenced, 
which,  considering  the  structure  of  the  caponniere,  and  the 
exposure  of  its  embrasures  to  the  enfilading  batteries,  will, 
in  all  probability,  take  place  at  an  early  period  after  this 
fire  is  opened. 


Pontalembeif  fj  |]oli)pnal  Dilcthol 


562...  Among  the  writers  on  permanent  fortification  wdiose 
works  have  had  an  important  bearing  on  the  progress  of 
the  art,  Montalembert  holds  a  conspicuous  place,  although 
not  educated  as  an  engineer.  Struck  by  the  evident  defects 
of  the  methods  of  his  predecessors,  particularly  the  want  of 
casemates,  both  for  defensive  dispositions  for  artillery  and 
musketry  and  the  shelter  of  the  garrison  and  munitions, 
Montalembert  devoted  his  time,  talents  and  fortune,  to 
bringing  about  a  change  in  the  .direction  in  which  it  seemed 
to  him  called  for.  His  efforts,  however,  led  to  no  modifica- 
tions of  consequence  during  his  life  (which  was  principally 
spent  in  angry  controversies  with  his  opponents),  except  the 
extension  of  casemated  defences  for  sea-coast  works;  and  it 


montalembert's  polygonal  method.  179 

is  only  within  a  comparatively  recent  period,  since  the 
termination  of  the  great  wars  in  Europe,  in  the  present 
century,  that  a  new  school  of  engineers  has  grown  up  in 
Germany,  based  upon  the  views  put  forth  mainly  by  Mon- 
talembert;  and  that  these  views  have  met  with  favor  in 
other  parts,  although  still  opposed  by  many  able  engineers, 
in  all  countries,  who  contest  their  soundness. 

5G3...The  [trincipal  propositions  of  Montalembert  consist 
in  the  entire  rejection  of  the  bastioned  system  as,  according 
to  his  views,  unsuitable  to  a  good  defensive  disposition ;  and 
in  its  stead  he  proposed  to  use  either  the  tcnaillcd  system  or 
the  polygonal  system;  in  basing  the  strength  of  these  last 
systems  upon  an  overwhelming  force  of  artillery  lire  in 
defensive  casemates,  and  in  organizing  strong  permanent 
works  within  and  independent  of  the  body  of  the  place, 
which  are  to  serve  as  a  secure  retreat  for  the  garrison  when 
forced  to  give  up  its  defence. 

564... Most  of  the  objections  urged  against  the  bastioned 
system  and  its  outworks  having  already  been  adverted  to  in 
the  analysis  of  the  front,  it  will  be  unnecessary  to  recapitu- 
late them  here;  and  as  the  tenailled  system,  composed  of 
faces  of  equal  lengths,  with  re-entering  angles  of  90°  and 
salient  angles  of  00°,  and  termed  by  Montalembert  perperi- 
(Ik-ular  fortification,  from  the  position  of  the  faces  at  the 
re-enterings,  has  many  obvious  and  more  serious  defects 
tlian  either  of  the  other  two ;  it  is  proposed  to  give  here  a 
description  of  the  polygonal  system  alone,  and  tliat  in  its 
most  simple  form:  the  one  in  which  Montalembert  pre- 
sented it  for  the  fortifications  at  Cherbourg,  one  of  the 
most  important  naval  stations  in  France. 

565. ..Montalembert  first  gave  the  name  polygonal  system 
to  a  tra^e  of  the  enceinte  in  which  all  of  the  angles  are 
either  salient,  or  where  the  re-enterings  are  very  slight. 
The  distinctive  features  of  his  method  are  shown  in  the 
works  which  he  projected  for  the  defence  of  the  harbor  of 
Cherbourg. 

506...  1 'lax.  In  the  tra96  proposed  for  this  place,  X  F, 
Fig.  1,  PI.  16,  is  the  exterior  side,  or  direction  of  the  scarp. 


180  montalembert's  polygonal  method. 

The  l)0(l3'  of  the  place  consists  of  the  scarp  wall,  D,  Y\g,.  1, 
and  section  on  P$,  arranged  with  casemates  for  artillery 
and  musketry;  of  a  corridor,  C,  between  these  casemates 
and  the  earthen  rampart  and  parapet,  B.  In  rear  of  the 
rampart  is  a  high  wall.  A,  arranged  M'ith  loop-holes,  within 
which  the  garrison  retires  Avhen  di-iven  from  the  defence  of 
the  rampart. 

567...Casemated  caponnieres,  Ji,  Avhich  are  secure  from  a 
coup  de  main,  are  placed  along  the  rampart,  and  so  arranged 
that  a  lire  can  be  thrown  from  them  over  the  parapet,  and 
also  along  the  terreplein.  The  corridor,  C,  is  also  swept 
by  a  casemated  caponniere,  G,  for  musketry,  and  the  front 
of  the  wall,  A,  by  a  like  arrangement. 

568. ..The  principal  caponniere  for  ilankingthe  main  ditch 
is  in  the  form  of  a  lunette,  and  placed  at  the  middle  of  the 
exterior  side,  its  flanks  joining  the  casemated  gallery,  D,  of 
the  enceinte.  The  flanks,  7/,  and  the  faces,  K,  of  this  work, 
are  arranged  with  two  tiers  of  artillery  and  musketry  fire, 
each  flank  carrying  ten  guns,  and  each  face  twelve  guns. 
A  wet  ditch,  /,  separates  the  faces  and  flanks;  a  loop-holed 
wall  encloses  the  portion  between  the  flanks,  from  which 
the  opposite  portion  between  the  faces  is  swept  by  mus- 
ketry. 

569. ..The  caponniere  is  covered  in  front  by  a  face  cover, 
iV,  of  earth  in  the  shape  of  a  redan.  The  scarp  of  the  en- 
ceinte is  covered  in  like  manner,  by  the  continuous  face 
cover,  0,  of  earth,  in  the  re-entering  angles  of  which,  case- 
mated  batteries  of  two  stories,  for  artillery  and  musketry, 
are  placed  to  flank  the  ditches,  and  sweep  the  positions  for 
counter-batteries  around  the  salients  of  the  covered-way. 
These  batteries  are  masked  in  front  by  the  earthen  works, 
S  and  Q.  The  whole  is  covered  by  the  covered-way,  ar- 
ranged in  the  usual  manner. 

The  better  to  flank  the  main  caponniere,  the  portion  of 
the  casemated  gallery  joining  it  is  arranged  with  two  tiers 
of  artillery  fire,  the  remaining  portion  having  but  one  tier 
of  guns. 

570.. .Profiles.     The  sections  along  P  Q,  B  S,  and  T  U, 


RECENT    GERMAN    FORTIFICATIONS.  181 

sliow  the  relative  command  of  the  different  works,  and  the 
width  of  the  ditches  and  earthen  ramparts. 

The  communications  between  the  different  works  are  by 
bridges  across  the  wet  ditches. 

571. ..It  is  now  admitted  on  all  hands  that,  althong-h  Mon- 
talembert  has  rendered  important  services  to  the  progress 
of  fortitication,  partii-uUirly  as  regards  the  more  extensive 
employment  of  casemated  defences,  still,  many  of  his  pro- 
jects were  visionarj-.  How  far  the  recent  works  constructed 
in  Europe,  which  are  based  on  his  views,  will  answer  their 
ends,  remains  to  be  seen  by  the  test  ot^-  actual  siege  opera- 
tions against  them. 

The  partisans  for  and  against  these  views  are  equally 
confidant  in  their  arguments;  but  \y\th  the  rapid  improve- 
ment in  artillery  which  has  taken  phice  within  the  last  few 
years,  and  the  heavier  calibre  which  will  doubtless  be  here- 
after used  in  siege  operation,  it  is  very  doubtful  Avhether, 
from  what  experience  has  already  shown  as  to  the  effects 
of  artiller\'  on  casemate  defences,  they  will  be  found  to 
withstand  these  powerful  means,  in  which  case  the  systems 
based  upon  JMontalembert's  view  must  fall  to  the  ground. 


Jlcrcnt  €»crnran  (Jjoi1i|irationfj. 


572... In  the  large  additions  made  to  the  fortifications  of 
the  Cernian  states  since  the  general  peace  in  Europe  in 
1815,  the  German  engineers  have,  for  the  most  part,  of 
these  new  structures,  embraced  the  ideas  put  forth  in  the 
works  of  Montalembert  and  Carnot,  adopting  for  the  plan 
of  their  enceintes  the  polygonal  system  with  flanking  cap- 
onnieres,  cond)ining  with  these  numerous  casemates  for 
defence,  for  l)<)ml)-proof  shelters,  for  ({uartcring  the  troops, 
and  preserving  the  munitions  and  other  stores. 


182  RECENT    (7ERMAX   FORTIFICATrOKS. 

573... From  what  has  been  published  on  this  subject  by 
the  German  engineei*s  themselves  and  other  European 
writers,  the  following  appear  to  be  the  leading  features 
upon  which  these  works  are  based : 

1st.  To  occupy  the  principal  assailable  points  of  the  posi- 
tion to  be  fortified,  b}^  works  which  shall  contain  within 
themselves  all  the  resources  for  a  vigorous  defence  by  their 
garrisons  ;  these  works  being  placed  in  reciprocal  defensive 
relations  with  each  other,  but  so  arranged  that  the  falling 
of  one  of  them  into  the  besieger's  hands,  will  neither  com- 
pel the  loss  of  the  others  nor  the  surrender  of  the  position. 

2d.  To  cover  the  space  to  the  rear  of  these  independent 
works,  either  by  a  continuous  enceinte,  usually  of  the  poly- 
gonal system,  with  a  revetted  scarp  of  sufhcicnt  height  to 
secure  it  from  escalade;  the  parts  of  this  enceinte  being  so 
combined  with  the  independent  works,  that  all  the  ap- 
proaches of  the  besiegers  upon  each,  both  during  the  near 
and  distant  defence,  shall  be  swept  in  the  most  eftective 
manner  by  their  fire ;  or  else  to  connect  these  works  by 
long  curtains;  or,  finally,  to  employ  these  works,  as  in  a 
system  of  detached  works,  either  to  occupy  important 
points  in  advance  of  the  main  work  or  for  forming  capa- 
cious entrenched  camps  with  a  view  to  the  eventualities  of 
a  war. 

3d.  To  provide  the  most  ample  means  for  an  active  de- 
fence by  covered- ways  strongly  organized  with  casemated 
redoubts,  and  with  spacious  communications  between  them 
and  the  interior  for  sorties  in  large  bodies. 

4th.  So  to  organize  the  artillery  for  the  near  defence  that 
it  shall  be  superior  to  that  of  the  besiegers  at  the  same 
epoch,  and  be  placed  in  positions  where  it  will  bo  sheltered 
from  the  besieger's  guns  up  to  the  time  that  it  is  to  be 
brought  into  play. 

574... Plan.  The  plan  of  the  independent  works  may 
be  of  any  polygonal  figure  which  is  best  adapted  to  the 
part  assigned  them  in  the  defence  of  the  position  ;  but 
they  are  generally  in  the  form  of  lunettes,  PI.  23,  Fig.  2, 
having  a  revetted  scarp  and  counterscarp  to  secure  them 


TvECENT    GERMAN    FORTIFICATIONS.  183 

from  escalade.  In  the  gorge  of  the  work  a  casemated 
defensive  barrack  is  phiced,  which  serves  as  a  rcduit  or 
keep ;  a  simple  loop-holed  wall,  which  is  flanked  by  the 
barrack,  closing  the  space  between  it  and  flanks  of  the 
work,  and  securing  the  latter  from  an  assault  in  the  rear. 
The  ditches  of  the  work  are  either  flanked  from  the  en- 
ceinte in  their  rear,  or,  when  the  work  is  a  detached  one, 
]>y  caponnicres,  or  counterscarp  galleries.  The  work  is 
usually  organized  with  a  covered-way,  having  one  or  more 
casemated  redoubts,  and  a  system  of  mines  both  for  the 
exterior  and  interior  defence. 

575. ..The  barrack  is  usually  arranged  for  two  or  three 
tiers  of  covered  Are,  and  an  upper  one,  with  an  ordinary 
parapet  and  terreplein,  on  which  the  guns  are  uncovered 
and  destined  for  the  distant  defence.  The  two  upper  tiers 
of  covered  Are  are  for  artillery,  to  sweep  the  interior  of  the 
work,  and  to  reach,  by  curvated  flres,  the  approaches  on  the 
exterior.  The  lower  tier  is  loop-holed  for  musketry  to 
sweep  the  interior.  The  barrack  is  surrounded  by  a  nar- 
row ditch  on  the  interior,  ami  this,  when  necessary,  is 
flanked  by  small  caponnieres  placed  in  it,  which  are  entered 
from  the  lowest  story.  The  barrack  communicates  with 
the  interior  by  a  door  at  some  suitable  point;  and  the 
communication  between  the  interior  of  the  work  and  the 
exterior  is  through  doors  in  the  wall  enclosing  the  gorge. 

576... Considerable  diversity  is  shown  in  the  proflles  of 
these  works.  They  usually  consist  of  a  parapet  and  ram- 
part, of  ordinarj'  dimensions,  for  the  uncovered  defence;  of 
scarps  either  partly  detached  and  loop-holed,  with  a  corri- 
dor between  them  and  tlie  })arapet ;  or  of  scarps  with 
relieving  arches  arranged  with  loop-holes  for  musketry;  or 
of  a  combination  of  these  two.  The  height  of  the  barrack, 
and  the  command  of  the  parapet  of  the  exterior  work  are 
so  determined  that  the  masonry  of  the  former  shall  be  per- 
fectly covered  from  the  direct  fire  of  artillery,  and  the 
exterior  be  perfectly  swept  by  the  artillery  of  the  work. 
The  portions  of  the  counterscarps  at  the  salients  are  also 


184  RECENT    GERMAN   FORTIFICATIONS. 

arranged  with  defensive  galleries  to  sweep  the  ditches — 
usually  with  musketiy,  but  in  some  eases  with  artillery. 

577... In  the  salient  angles  of  the  work  casemates  are 
arranged  for  mortars,  to  fire  in  the  direction  of  the  capi- 
tals ;  and  one  or  more  casemated  traverses  are  placed  on 
the  terreplein,  to  obtain  a  fire  on  the  exterior  and  to  cover 
the  terreplein  from  ricochet.  The  masonry  of  these  trav- 
erses is  masked  by  the  parapet. 

578... Posterns  lead  from  the  interior  of  the  work  to  the 
scarp  galleries,  the  corridors,  the  ditch  caponnieres  and  the 
casemated  mortar  battery  in  the  salient. 

579... The  system  of  mines  for  the  exterior  defence  con- 
sist simply  of  listening  galleries  leading  outward  from  the 
counterscarp  galleries.  That  for  interior  defence  is  simi- 
larly arranged ;  the  communications  with  it  being  either 
from  the  barrack  caponnieres  or  from  the  counterscarp  of 
its  ditch. 

580... The  work  is  provided  with  powder  magazines, 
which  are  placed  at  the  points  of  the  interior  least  exposed 
to  the  enemj^'s  fire  ;  and  covered  guard-rooms,  store-rooms 
for  mining  tools,  etc.,  are  made  in  connection  with  the 
posterns. 

581... Profiles.  In  the  profiles  of  their  works,  the  Ger- 
man engineers  follow  nearl}'  the  same  rules  for  the  forms 
and  dimensions  of  their  parapets  as  those  in  general  use  in 
other  services.  They  employ  three  kinds  of  scarp  revete- 
raents :  1st,  the  ordinary  full  revetement,  PI.  20,  Fig.  1,  or 
sustaining  wall,  with  counter-forts;  2d,  revetements  with 
relieving  arches,  PI.  21,  Figs.  1,  2,  either  with  or  without 
defensive  dispositions,  as  circumstances  may  demand ;  3d, 
scarp  walls,  either  partly  or  wholly  detached  from  the  ram- 
part and  parapet.  In  all  of  these  cases,  they  give  to  their 
scarp  walls  a  height  from  27  to  30  feet  for  important  works, 
and  about  15  feet  for  those  less  so.  The  batter  of  these 
walls  is  usually  one  base  to  twelve  perpendicular.  For  the 
full  revetement  with  counter-forts,  they  regulate  the  dimen- 
sions of  both  so  as  to  afford  the  same  stability  as  in  the 
revetements  of  Vauban. 


RECENT    GERMAN    FORTIFICATIONS,  185 

582. ..In  their  revetements  Avith  simple  rcUeviiig  arclies, 
they  use  either  one  or  two  tiers  of  urches;  phicing  the  sin- 
gle tier  either  near  the  top  or  toward  the  middle  of  the 
wall,  according  to  the  nature  of  the  soil  and  the  pressure 
to  be  sustained. 

583...Revetements  Avith  relieving  arches  for*detence,  or 
scarp  galleries,  are  arranged  for  one  or  two  tiers  of  tire. 
The  back  of  the  galler}^  is  sometimes  left  open,  the  earth 
falling  in  the  natural  slope  in  the  rear;  or  it  is  enclosed 
either  with  a  plane  or  a  cylindrical  wall,  according  to  the 
pressure  to  be  sustained. 

584... When  the  upper  part  of  the  wall  is  detached,  PL 
20,  Fig.  7,  to  form  a  corridor  between  it  and  the  parapet  in 
its  rear,  the  top  portion  alone  is,  in  some  cases,  arranged 
with  loop-holes  and  arcades,  or  with  recesses  to  their  rear, 
to  cover  the  men  from  shells;  in  others,  a  scarp  gallery  is 
made  below  the  floor  of  the  corridor  to  give  two  tiers  of 
lire.  The  corridors  are  from  8  to  20  feet  in  width,  and 
when  deemed  requisite  they  arc  divided,  from  distance  to 
distance,  by  transverse  loop-holed  traverse  walls  for  defence. 

585... When  the  scarp  walls  are  entirely  detached,  PL  20, 
Figs.  4,  5,  6.  they  are  arranged  for  either  one  or  two  tiers 
of  fire,  Avith  arcades  to  cover  the  men ;  the  banquette-tread 
of  the  upper  tier  of  loop-holes  resting  on  the  arches  of  the 
lower  tier  of  arcades. 

586... The  counterscarps  are  revetted,  either  with  the 
ordinary  wall,  or  ai-ranged  Avitli  a  defensive  gallery,  Avith 
a  full  centre  arch,  parallel  to  the  face  of  the  counterscarp 
wall. 

587. ..The  German  engineers  make  a  lil)eral  use  of  bomb- 
proof casemates  for  mortar  and  gun  batteries.  The  former 
are  either  placed  in  the  rear  of  the  parapet,  or  of  the  ram- 
l)art,  and  along  the  faces,  or  else  in  a  salient  angle.  In  the 
former  case  tliey  are  covered  in  front  b}^  the  parapet,  in  the 
latter  either  by  the  scarp  Avail  alone  or  by  a  casemated 
defensiA'e  mask  placed  in  front  of  the  battery.  When 
]»laced  along  a  face,  PL  20,  Fig.  0,  they  arc  arranged  for 
one  or  several   mortars,  and   frequently  Avith  two  tiers  of 


186  RECENT    r.EUMAX    FORTIFICATIONS. 

arches,  tlic  upper  one  for  the  service  of  tlie  mortar  and 
tlie  lowei-  one  for  a  l)onil)-proof  shelter  for  troops  oi-  muni- 
tions. The  ehaniber  oecnpied  l)y  eaeh  mortar  is  ii  ree- 
tangle,  12  feet  wide,  and  about  20  feet  in  depth;  this  is 
covered  by  a  full  centre  rampart  aivh.  the  heiu'lit  of  the 
piers  at  the^jack  of  the  chamber  beini::  4  feet,  and  in  front 
from  G  to  9  feet  al)ove  the  level  of  the  mortar  platform. 
This  enables  the  sliell  to  clear  the  top  of  the  parapet  in 
front,  ■which  is  about  12  feet  above  the  level  of  the  plat- 
form, and  21  feet  in  front  of  the  battery.  The  chamber  is, 
in  some  cases,  left  open  both  in  front  and  rear,  to  allow  the 
smoke  to  escape  readily  and  to  diminish  the  etfect  of  the 
concussion  of  the  discharge  on  the  masonry;  in  other  cases 
it  is  closed  by  a  wall  in  the  rear — an  opening  being-  left  in 
this  wall,  immediatel}'  under  the  arch,  fov  the  same  i)ur- 
pose.  A  small  ditch  is  [)laced  in  front  of  the  battery;  and 
the  wall  in  front  is  extended  about  3  feet  above  the  plat- 
form, to  shelter  the  men  from  the  explosion  of  shells  that 
may  fall  into  the  diteh.  The  abutments  of  the  arches  are 
7  feet  thick,  and  the  piers  4  feet.  The  arches  are  2  feet  6 
inches  thick ;  they  are  covered  on  top  by  from  4  to  6  feet  in 
thickness  of  earth;  and,  in  like  manner,  the  arch  and  abut- 
ment are  secured  on  the  side  exposed  to  an  eniilading  tire. 
An  ordinary  traverse  is  placed  on  the  same  side,  to  cover 
the  masonr}^  and  communication  between  tlie  front  of  the 
battery  and  the  parapet ;  the  chambers  of  the  mortars  are 
entered  from  the  front,  or  from  the  sheltered  side,  by  a 
door  in  the  abutment. 

.588. ..When  placed  in  an  obtuse  salient,  PI.  21,  Figs.  8,  4, 
behind  a  scarp  with  a  corridor,  a  space  of  10  or  12  feet  is 
left  between  the  back  of  the  scarp  wall  and  the  front  of  tlu^ 
battery.  The  platforms  of  the  mortars  are  about  the  same 
distance  below  the  top  of  the  scarp.  The  arches  are  cov- 
ered by  the  earth  of  the  para[)et,  to  the  depth  of  o  or  6  feet. 
The  dimensions  and  arrangement  of  the  chambers  and 
arches  are  the  same  in  this  as  in  the  preceding  case.  The 
communieation  from  the  interior  of  the  work  to  the  battery 
is  by  a  postern,  0  feet  in  width.     A  casemated  guard-room 


RECENT    GERMAN    FORTIFICATIONS.  187 

• 

is  made  in  connection  with  the  postern ;  and  M^hcn  the 
scarp  is  ai'ranged  with  relieving  arches,  either  for  defence, 
or  for  other  pnrposes,  an  arclied  stairway  is  in  some  cases 
made  as  a  communication  from  tlic  postern  to  the  case- 
mates. A  transverse  wall  with  a  door-way,  serves  to  cut 
off  the  court  in  front  of  the  battery  from  Hhe  corridor  to 
the  rear  of  the  wall. 

589. ..In  the  less  obtuse  salients,  the  front  of  the  batterj- 
is  made  circular ;  the  chambers  being  so  placed  that  the 
fire  of  the  mortars  can  l)e  thrown  in  the  direction  of  the 
capital.  A  casemated  defensive  traverse,  placed  in  the 
salient,  masks  the  battery  in  front,  and  it  is  covered  on  the 
ilanks  by  the  earth  on  the  top  of  the  arches.  The  details,' 
otherwise,  are  the  same  as  in  the  preceding  case. 

590... In  the  arrangement  of  casemated  traverses  for 
guns,  PI.  20,  Figs.  10,  11,  12,  the  chamber  for  each  gun  is 
a  rectangle,  24  feet  in  depth,  estimated  from  tlie  interior 
crest  of  the  parapet,  and  12  feet  wide.  The  chamber  is 
covered  by  a  full  centre  arch,  the  height  from  tlie  level  of 
the  platform  to  the  crown  of  the  arch  being  8J  feet.  The 
arch  is  2  feet  thick,  the  piers  between  the  arches  3  feet, 
and  the  abutments  3J  feet.  The  mask  wall  in  front  of  the 
chamber  is  3  feet  thick.  This  wall  is  covered  in  front  by 
the  parapet,  and  by  several  layers  of  fascines  or  of  heav}- 
timber,  laid  across  the  embrasure  in  the  parapet  and  above 
the  one  through  the  mask  wall.  The  cheeks  of  the  embra- 
sure in  the  parapet  are  likewise  revetted  with  heavy  tim- 
ber, to  some  distance  in  front  of  the  nuisk  wall.  The 
masonry  is  covered  on  top  and  on  the  sides  with  5  or  6  feet 
thickness  of  earth,  to  secure  it  from  shells  and  enfilading 
shot.     The  casemates  are  left  o]ten  to  the  rear. 

591. ..In  some  cases,  a  blinded  Itattery  for  a  single  gun, 
PI.  20,  Fig.  12,  is  arranged  by  enclosing  the  sides  and  front 
of  the  cliamber  witli  walls,  and  covering  it  with  a  layer  of 
heavy  timber,  supporting  two  thicknesses  of  large  fascines, 
covered  with  a  thickness  of  5  or  6  feet  of  eartli.  Tlio 
dimensions  of  the  chamber  are  the  same  as  in  the  preced- 
inir  case. 


188  RECENT    GERMAN    FOKTIFrCATIONS. 

592...TI10  capoiuiicres,  I'l.  21.  Vltrs.  8,  0,  10.  for  ilaiiking 
the  main  ditcli,  usually  consist  of  two  faces  and  two  case- 
matod  tlank  l)attcries  of  two  stories  each ;  tlie  lower  story 
being  loop-holed  for  musketry  and  the  upper  pierced  for 
artillery.  Eacli  battery  consists  of  several  rectangular 
clnunbers,  each  chamber  for  a  single  gun  being  12  feet 
wide  and  24  feet  deep,  or  of  smaller  dimensions,  accord- 
ing to  tlie  calibre  of  the  gun  and  the  kind  of  ca,rriage  on 
which  it  is  mounted.  The  upper  chambers  are  covered 
with  bomb-proof  arches,  the  lower  one  by  arches  of  suffi- 
cient strength  for  the  weight  thrown  upon  them.  The 
front  mask  wall  of  the  casemates  is  6  feet  thick;  the  wall 
in  rear  is  3  feet  thick,  and  is  pierced  with  windows  for 
light  and  ventilation.  Openings  for  tiie  escape  of  the 
smoke  are  also  made  in  the  front  mask  wall,  immediately 
below  the  crowns  of  the  arches.  An  interior  court  30 
feet  in  width  is  left  between  the  two  Hank  batteries,  and 
wIk'11  the  batteries  are  detached  from  the  scarp  wall,  the 
space  between  is  enclosed  by  a  loop-holed  wall  built  on 
each  side  in  the  prolongation  of  the  front  mask  wall. 

593. ..The  faces  of  the  eaponniere  form  a  salient  of  60°. 
They  are  separated  from  the  flanks  by  two  stories  of  arched 
corridors,  in  front  of  which  arc  two  arched  chambers  of  two 
stories,  the  upjter  chamber  being  arranged  for  mortars. 
An  open  triangular  court  is  left  between  tlie  front  walls 
of  these  chambers  and  the  faces  of  the  caponnit^re.  The 
upi)er  part  of  the  walls  of  the  faces,  along  this  court,  are 
arranged  with  arcades  and  loop-holed  for  mu.sketry,  and 
liave  an  o})en  corridor  in  their  rear  on  the  same  level  as 
tlie  chambers  of  the  second  story. 

594. ..The  eaponniere  is  provided  with  a  [)owder  magazine 
and  other  necessary  conveniences  for  the  defence. 

595. ..The  flanks  of  the  caponniiirc  and  its  interior  are 
swept  by  the  musketry  of  the  scarp  galleries  in  its  rear. 
The  faces  in  like  manner  are  swept  by  artillery  and  mus- 
ketry in  casemates  behind  the  scarp. 

The  arclied  chambers  of  the  upper  story  are  covered  by  a 
thickness  of  5  or  6  feet  of  earth. 


RECENT    GERMAN    FORTIFICATIONS.  189 

50G...Capoi)inei'es  of  smaller  dimensions,  termed  hastion- 
iKts,  V\.  22,  Fig.  1,  placed  at  the  angles  of  redoubts  to  Hank 
the  ditches,  are  usually  arranged  for  musketry,  but  some- 
times receive  artillery.  Those  for  flanking  the  ditches  of 
the  independent  works  in  advance  of  the  enceinte  are  some- 
times placed  in  the  ditches  of  these  works,  sometimes  behind 
the  scarp  wall  of  the  enceinte,  and  sometimes  in  casemates 
in  the  main  ditch,  detached  from  the  scarp  wall. 

597...The  conununirations  from  the  interior  with  the  cap- 
onnicres  are  by  posterns. 

.598... The  defensive  barracks,  PL  21,  Figs.  6,  7,  forms  one 
of  the  most  distinctive  features  in  the  organization  of  the 
German  fortifications.  The  plan  of  these  works  may  be  of 
any  figure  to  suit  the  object  to  be  subserved  by  them.  When 
placed  in  the  gorge  of  an  independent  work  and  servino-  as 
a  keep  to  it,  their  plan  is  usually  semicircular. 

599... The  barrack  consists  of  one  or  two  stories  of  arched 
chambers  for  covered  fire  and  an  open  battery  on  top,  with 
an  earthen  parapet  and  terreplein. 

600. ..The  arched  chambers  are  formed  by  connecting  the 
front  and  rear  walls  of  the  barrack  by  transversal  walls, 
which  serve  as  piers  for  the  arches  of  the  ceiling,  the  soflits 
of  which  are  either  cylindrical  or  conoidal,  according  as  the 
piers  are  parallel  or  otherwise.  The  chambers  are  about  18 
to  20  feet  wide  and  60  feet  in  depth  ;  tlieir  height,  under 
the  crown  of  the  arch,  from  9  to  11  feet.  The  arch  of  the 
liighest  chamber  is  2i  feet  thick,  and,  being  covered  with  a 
cap[.ing  and  the  earth  of  the  open  battery  on  top,  is  bomb- 
proof; the  arches  of  the  lower  stories  are  li  feet  thick. 
The  front  wall  of  the  barrack  is  usually  6  feet,  and  is 
pierced  in  each  chamber  with  one  eml)rasure  and  two  loop- 
holes. The  rear  wall  is  3  feet  thick,  and  lias  a  window  in 
each  chamber  for  light  and  ventilation.  Openings  for  ven- 
tilatioji  are  also  made  in  the  front  wall,  just  beneath  the 
crowns  of  tlie  arches.  Door-ways  are  made  through  the 
transversal  walls  to  form  a  communication  between  all  the 
chambers.  Tliese  arc  somctiniCH  placed  along  the  centre  of 
the  piers,  at  others  near  their  extremities,  so  tliat  the  cham- 


190  RECENT    CERMAN    FORTIFICATIONS. 

bers  being  dividt-d  l>y  sHglit  partitions  into  two  compart- 
iiK'iits.  for  tliG  quartorini!;  of  the  troops,  tliore  will  be  a 
rdhtinuous  hall  cither  along  the  centre  oi-  near  the  rear 
Avail,  upon  which  ;dl  the  a]»artnient.s  open.  The  hai'raeks 
are,  otherwise,  arranged  with  all  the  re(piisites  for  loilging 
tlie  troops  comfortably  and  healthfully.  The  lower  story  of 
the  barrack  is  surrounded  by  a  narrow  ditch.  A  draw- 
bi-idge  across  this  ditch  secures  the  entrance  to  the  barrack 
at  the  gorge. 

G01...In  some  cases,  PI.  21,  Fig.  5,  where  the  fn)nt  wall 
of  the  barrack  is  much  exposed  to  the  besieger's  fire,  the 
piers  are  made  thicker  near  the  front  wall  ;  and  they  each 
liave  two  vertical  grooves  to  receive  timber,  laid  hori/,on- 
tally,  between  which  sand-bags  can  be  packed  in  to  atlbrd 
shelter  when  the  front  wall  has  become  much  damaged  by 
the  besieger's  artillery. 

602. ..The  foregoing  summary  description,  with  the  [ihites, 
will  give  a  good  general  idea  of  the  princi}>al  defensive  ar- 
rangements, constructed  of  masonry,  which  enter  so  largely 
into  the  recent  German  fortifications,  and  u[ioii  the  details 
of  which  the  (icrman  engineers  have  bestowed  great  atten- 
tion. 

G03...The  adoption  of  the  polygonal  system,  with  cajjon- 
niere  defences  for  the  main  ditch,  has  enable(l  the  (Jerman 
engineers  to  give,  in  their  fortifications,  a  greater  exterior 
side  than  in  the  bastioned  system  generally,  and  still  admit 
of  lines  of  defence  in  which  grape,  canister  and  small  arms, 
particularly  the  later  im[troved  musket,  will  tell  with  effi- 
cacy upon  the  besieger's  works  on  the  glacis  around  the 
salients  of  the  enceinte.  With  a  few  exceptions,  nothing 
of  a  very  reliable  character  has  been  }»ublished  as  to  the 
trace  of  these  works,  further  than  the  general  defensive 
dispositions.  From  tliese  it  appears  that,  keei)ing  in  view 
the  cardinal  point  in  all  I'ortiiicatioii,  the  adaptation  of  the 
various  fronts  to  the  site  of  the  work,  sc»  that  all  the 
a}iproaches  upon  them  shall  be  comnunided  and  swept 
by  their  lires,  whilst  the  jirincipal  lines  of  the  enceinte 
receive  the  best  direction  to  place  them  as  little  as  possible 


FRONTS    OF    POSExV.  191 

witliin  the  range  of  eniilading  positions,  tlic  exterior  side 
is  usually  kept  somewhere  between  400  and  600  French 
metres,  or  between  450  and  700  yards. 


^jrontfj  4  i^'j^^^* 


G04...Tlie  following  is  an  outline  of  the  tra(;e  and  defen- 
sive disjiositions  of  a  front  of  the  fortilications  of  Posen, 
one  of  the  most  noted  of  these  recent  structures.  The 
exterior  side,  A  B,  PI.  22,  Fig.  2,  is  580  yards;  a  distance, 
C  D^^\  A  i?,  is  set  oft'  on  the  perpendicular  of  the  front 
and  within  it;  and  ou  the  line  joining  the  salients  J.,  B 
with  Z>,  distances,  A  ii,  B  3f,  equal  |  A  B,  being  set  off 
give  the  faces  of  the  front.  The  salient,  JE,  of  the  inde- 
pendent work  is  on  the  peipendicular  of  the  front,  and  at  a 
distance  from  C  equal  to  ^A  B.  Describing  from  E  nw  arc 
with  a  radius  of  20  yards,  and  drawing  tangents  to  it  from 
the  })oints  7/ and  31^  gives  the  counterscarps  of  the  inde- 
pendent work;  the  faces,  E  E,  E  F',  are  parallel  to  the 
counterscarp,  and  equal  to  \  A  B.  The  ditches  of  this 
work  are  flanked  l)y  casemated  caponnieres,  H I^  31  N, 
wbich  are  35  yards  in  length,  or  sufficient  for  four  guns. 
Tlie  directions  of  these  flanking  casemates  being  nearly 
perpendicular  to  the  direction  of  the  faces  E E,  E  F'.  Tbe 
flanks,  E  6r,  E  G\  receive  the  most  suitable  directions  for 
s\vee[)ing  the  api»roaches  in  advance  of  the  salients  of  the 
front.  The  main  ditch  is  about  30  yards  wide,  its  coun- 
terscarp being  i>arallel  to  the  faces  of  tljc  enceinte,  and  the 
gorge  of  the  independent  work  is  on  the  prolongation  of 
tills  counterscarp.  The  curtains  of  the  enceinte  are  di- 
rected from  the  points  /,  iV,  on  the  point  C,  and  are  thus 
nearly  parallel  to  the  exterior  side.  The  main  ditch  is 
flanked  by  a  large,  casemated,  defensive  barrack,  having 


102  FRONTS    OF    POSEN. 

three  stories  of  covered  fire,  the  lower  for  musketry  and 
tlie  upper  for  artillery,  and  an  open  battery  on  toj).  The 
plan  of  this  work  is  that  of  the  letter  U:  the  circular  part 
projects  within  the  independent  work,  and  serves  as  its 
keep;  the  sides  arc  nearly  perpendicular  to  the  faces  of  the 
encointc  and  are  prolonged  within  the  enceinte,  serving  as 
a  defensive  caponniere  to  flank  the  main  ditch,  to  sweep 
the  terreploins  of  the  enceinte  curtains,  and  also  the  in- 
terior, within  the  range  of  the  guns  of  two  round  towers 
M'itli  which  the  sides  are  terminated.  The  sides  of  the 
barrack  are  separated  from  the  rampart  of  the  curtain  by 
lateral  ditches  10 yards  wide,  which  give  access  to  the  main 
ditch  from  the  interior  for  troops  in  large  bodies  for  sorties. 
The  parapet  of  the  enceinte,  PI.  20,  Fig.  4,  is  thrown  back 
from  the  scarp,  leaving  a  corridor  l)etween  the  foot  of  its 
exterior  slo[)e  and  the  scarp  wall,  the  floor  of  which  is 
12  feet  above  the  bottom  of  the  main  ditch.  The  scarp 
wall  rises  16  feet  above  the  level  of  the  floor,  thus  giving  it 
a  total  height  of  28  feet  above  the  bottom  of  the  main 
ditcli.  This  wall  is  loop-holod  for  small  ai-ms.  Tlic  coun- 
terscarp wall  of  the  main  ditch  is  24  feet  in  height.  The 
faces  and  flaidcs  of  the  enceinte  have  a  relief  of  44  feet; 
the  relief  of  the  curtain  being  only  40  feet.  The  corridors 
of  the  curtain  terminate  at  the  court  or  open  space  behind 
the  flankiuff  casemates,  II  I,  M  N.  Posterns  lead  from  the 
interior  to  the  corridors  of  the  fiices  and  flanks,  and  from 
the  lateral  ditches  to  the  corridors  of  the  curtain.  The 
interior  open  space  between  the  sides  of  the  del'ensive 
barrack  is  closed  by  a  lo(^p-holed  wall  between  the  end 
towers.  A  dit<'h  sun-ounds  the  towers  and  the  gorge 
between  them,  across  which  a  bridge,  tei'minated  at  the 
wall  by  a  draw,  gives  access  to  the  interior  open  space  and 
the  barracks. 

60;'). ..The  scarp,  rampart  and  parapet,  PI.  22,  Fig.  5, 
of  the  independent  work,  are  arranged  with  a  profile  simi- 
lar to  that  of  the  enceinte.  The  circular  })ortion  of  the 
defensive  barrack  which  serves  as  the  keep,  is  surrounded 
by  a  ditch,  which  is  swept  hy  small  caponnieres  attached 


FORT   ALEXANDER.  193 

to  the  keep.  A  circular  mortar  battery,  covered  in  front 
by  a  casemated  traverse,  is  placed  in  the  angle  of  this 
work,  and  behind  this  a  casemated  battery  for  howitzers  is 
placed  on  its  terreplein,  in  the  direction  of  its  capital,  to 
give  reverse  views  on  the  glacis  of  the  collateral  indepen- 
dent works.  The  gorge  of  this  work  is  closed  by  a  loop- 
holed  wall  which  extends  between  the  keep  and  the  scarp 
wall  of  the  tlaidvs.  The  communication  between  the  main 
ditch  and  the  interior  is  through  a  gate-way  in  this  wall. 
Posterns  lead  from  the  interior  to  the  corridors  of  the  faces 
and  Hanks,  and  to  the  mortar  battery  in  the  salient. 

GOG. ..The  counterscarp  of  the  independent  work  is  ar- 
ranged with  a  defensive  gallery,  with  which  a  system  of 
mines  for  the  exterior  defence  is  connected.  A  system 
of  mines  for  the  interior  defence  is  connected  with  the 
small  caponnieres  in  the  ditch  of  the  keep. 

GOT. ..The  covered-way  is  w'ithout  the  usual  traverses,  its 
interior  crest  being  broken  into  a  cremaillere  line.  Its  sa- 
lient and  re-entering  places  of  arms  are  occupied  by  case- 
nuited  redoubts.  The  communications  from  the  nuiin  ditch 
to  the  covered-way  are  by  wide  ramps,  which  are  at  the 
gorges  of  the  re-entering  places  of  arms,  and  under  the  lire 
of  their  redoubt.'^. 


<Jort  ^lc^;uulcr. 


608. ..Among  the  most  reliable  of  tlie  tra(,-es  published 
of  German  fortification,  is  that  of  the  main  front  of  Fort 
Alexander,  a  detached  quadrilateral  work  of  tlie  ftrtifica- 
tions  of  Coblentz,  given  in  tlie  description  of  these  fortifi- 
cations by  Col.  Iluniphrey. 

()0<>...Plan.  The  exterior  sides  of  the  enceinte  of  this 
fort,  IM.  22,  Fig.  6,  form  a  parallelogram,  the  acute  angles 
1:3 


104  FORT    ALEXANDER. 

(^f  Avliicli  arc  85°..  The  main  and  roar  IVdnts  arc  oadi  500 
yards,  and  tlie  other  two  420  yards  each.  The  main  front 
is  of  the  polygonal  system,  ■with  a  strong  defensive  capon- 
nicre  to  flank  the  main  ditch.  The  caponniiire  is  covered 
by  a  demilune,  and  the  salients  of  the  enceinte  by  counter- 
guards;  the  ditches  of  these  works  l)eing  flanked  by  case- 
mated  liatteries  at  the  re-entering  formed  between  them. 
There  is  no  covered-way  in  front  of  these  outworks,  their 
counterscarps  being  of  earth,  with  a  gentle  slope.  A  small 
earthen  work,  containing  a  casemated  redoubt,  is  thrown 
up  at  the  salients  of  the  counterguard  counterscarp, 

610... To  construct  the  trace,  take  rt  6=500  yards,  for  the 
exterior  side  of  tlie  enceinte,  which  divide  into  three  equal 
parts,  ftrf=(ie=e6.  Bisect  a  6  by  a  perpendicular,  on  which 
set  oflt"  hll=hd=^he=^  ah.  Through  H,  drawing  a  paral- 
lel to  a 6,  and  setting  off  along  it  the  distances  II  A^lIB 
=320  yards,  the  points  A  and  B  will  be  the  salients  of  the 
counterguards. 

611. ..From  11  as  a  centre,  with  the  radii  Hil^  He,  de- 
scribe two  arcs,  on  which  set  off  from  d  and  c  the  chords, 
di—ek=SS  yards,  these  will  be  the  lengths  of  the  case- 
mated  flanks;  ik  being  joined,  gives  the  enceinte  curtain. 
The  salient  angle  of  the  main  caponniere  is  constructed  by 
drawing,  from  a  point,  w,  on  the  capital,  at  a  distance  of 
20  j'ards  from  the  lines,  lid,  He,  lines  to  the  extremities,  i 
and  /.-,  of  the  casemated  flanks.  The  flanks  of  the  capon- 
niere, in=^vo,  extend  back  to  the  exterior  side,  and  are  33 
yards  in  length  and  33  yards  apart,  or  each  16 J  yards  on 
each  side  of  the  capital.  The  faces  of  the  counterguards 
are  directed  on  a  point,  C=l  A  B—5Sh  yards  on  the  capi- 
tid  iVom  H  The  salient,  F,  of  the  demilune  is  ^  A  .5=106 
yards  from  the  point  C;  its  faces,  FH,  F E,  are  parallel 
to  the  lines  lid.  He,  wdiich  last,  joined  by  an  arc  of  a 
circle,  described  from  m  as  a  centre,  with  a  radius  of  20 
yards,  and  terminated  at  the  counterscarp  of  the  enceinte 
ditch,  which  is  28  yards  from  ah,  will  give  the  demilune 
gorge.  A  casemated  battery  for  three  guns,  behind  the 
dcmihuie   scarp   wall,  flaidvs  the   counterguard   ditch,  and 


FORT   ALEXANDER.  195 

one  for  three  guns  flanks  the  demilune  ditch,  and  closes 
the  opening  between  the  demilune  and  counterguard  at 
this  i»oint.  A  narrow  ditch,  10  feet  wide,  is  left  between  the 
flank  of  this  battery  and  the  extremity  of  the  counterguard, 
as  a  communication  between  tlie  main  ditch  and  the  ditches 
of  the  outworks.  This  opening  is  masked  by  an  overlap  of 
the  counterguard. 

612...Casematcd,  or  blinded  batteries,  arc  made  in  the 
salients  of  the  enceinte  and  of  the  demihme. 

613. ..Profiles.  The  main  caponniere.  Fig.  8,  has  two 
tiers  of  covered  artillery  fire  on  the  flanks,  of  five  guns 
each ;  the  lower  to  sweep  the  main  ditch,  the  upper  the  ter- 
repleins  of  the  countcrguards;  its  faces  have  two  tiers  of 
loop-holes.  It  has  no  uncovered  fire,  but  a  simple  coverino- 
of  earth  as  a  bomb-proof. 

614... Casemates,  for  live  mortars  each,  are  placed  in  the 
salients  of  the  enceinte,  at  the  foot  of  the  rampart  slope. 

615... A  narrow  corridor.  Fig.  6,  the  floor  of  which  is  20 
feet  above  the  bottom  of  the  main  ditch,  is  left  behind  the 
scarp  wall  of  the  enceinte,  the  faces  and  curtains  of  this 
wall  are  loop-holed,  and  arranged  with  arcades  to  shelter 
the  men,  like  the  detached  scarp  walls  of  Carnot.  These 
scarps  are  30  feet  high.  The  command  of  the  enceinte 
over  the  parade  is  26  feet. 

616. ..The  scarp  walls  of  the  demilune  and  countcrguards, 
Fig.  7,  are  arranged  like  those  of  the  enceinte.  Tlie  com- 
mand of  these  works  is  16  feet.  Their  counterscarps  are 
arranged  with  loop-holed  galleries,  from  which  communi- 
cations lead  to  a  system  of  mines  for  exterior  and  interior 
defence. 

617... The  rear  side  of  this  fort,  not  being  exposed  to 
artillery,  is  simply  closed  by  a  loop-hoped  wall  and  ditch. 
A  large,  circular,  defensive  barrack  occupies  the  centre  of 
this  rear  front,  serving  as  a  keep  to  the  fort,  and  to  sweep 
by  its  fire  the  ground  on  the  rear  and  flanks  of  the  front. 

618. ..It  will  be  seen  that,  in  the  arrangement  of  the 
plan  of  this  work,  the  polygonal  system,  with  caponniere 
defences,  of  Montalembert,  has  been  adopted  as  the  basis. 


196  WORK    AT    OERMERSHEIM. 

Avitli  siieli  modifications  as  the  features  of  tlic  site  afforded, 
to  witlidrnw  the  principal  lines  from  the  range  of  the  enfi- 
ladinsr  views  from  without. 


Wi^r\\  at  (5urmerf3hcim. 


619... In  the  organization  of  works  with  wet  ditches,  the 
German  engineers  adopt  the  same  general  disposition  of 
the  elements  of  a  front  as  they  do  in  dry  ditches;  occupying 
the  most  important  points  of  the  polygon  to  he  enclosed  hy 
independent  works,  and  composing  the  enceinte  of  fronts 
of  the  polygonal  system :  taking  their  exterior  sides  between 
the  limits  of  350  and  650  yards,  and  sweeping  the  main 
ditch,  and  the  positions  for  the  besieger's  breaching  batter- 
teries  around  the  salients  of  the  enceinte,  by  the  iianks  of  a 
defensive  caponniere.  The  following  concise  description 
of  a  front  of  the  te(e  de  poni  opposite  Germersheim,  will 
give  a  good  idea  of  the  general  defensive  arrangements  in 
such  cases. 

620... Plan.  The  front,  XY,  PI.  33,  Fig.  1,  is  a  tenailled 
line  Avitli  a  slight  re-entering  at  the  centre  of  the  exterior 
side.  The  salients  of  the  front  are  occupied  by  small  bas- 
tions, with  a  scarp  gallery  on  the  faces  and  flanks,  and 
having  its  gorge  closed  by  a  loop-holed  wall,  with  a  defen- 
sive, casemated  reduit  at  its  centre. 

621... The  centre  of  the  front  is  occupied  by  a  capacious, 
casemated  edifice,  which  extends  from  the  interior  of  the 
gorge  of  the  independent  work,  across  the  main  ditch,  to 
within  the  enceinte.  The  circular  portion  of  this  edifice, 
within  the  independent  work,  has  two  tiers  of  covered  fire, 
with  an  o}>en  battery  on  top,  and  serves  as  the  reduit  of 
this  work.     The  central  portion  has  two  tiers  of  covered 


WORK    AT    GERMERSIIEIM.  197 

fire,  and  serves  as  a  capoiinicre  for  sweeping  the  main 
ditch,  etc.  Underneath  this  portion  are  arched  passages,  to 
communicate  by  water  between  the  ditch  on  each  side  of 
the  caponniere.  The  part  of  the  edifice  within  the  enceinte 
is  a  defensive  barrack,  with  three  tiers  of  covered  fire,  and 
an  open  battery  on  top,  from  Avhich  the  terreplein  of  the 
enceinte  curtain,  the  gorges  of  the  bastions  and  tlie  glacis 
of  tlie  enceinte  can  he  swept. 

G22...The  enceinte  curtain  is  not  revetted  with  masonry. 
The  exterior  sk)pe  of  its  parapet  descends  to  a  wide  berm 
several  feet  above  tlie  water  level  of  the  wet  ditch,  and 
which,  in  many  places,  is  planted  with  a  thorn  thickset 
hedge  as  an  obstacle  to  an  assault.  The  rampart  of  the 
curtain  is  sustained  within  by  a  high  wall,  which  joins  the 
loop-holed  walls  of  the  bastion  gorges,  and  is  flanked  by 
the  bastion  r^duits. 

623. ..The  independent  work  is  in  the  form  of  a  lunette: 
its  faces  being  divided  into  three  parts,  each  with  a  greater 
command  than  the  one  in  its  rear.  The  profile  of  this  work 
is  like  that  of  the  enceinte  curtain  ;  its  ditches  are  dry, 
their  bottoms  being  slightly  above  the  water  level  of  the 
nniiu  ditch.  The  ditches  are  flanked  by  casemated  capon- 
nieres  which  extend  across  them  to  the  gorges  of  the  re- 
entering [daces  of  arms,  for  which  works  they  also  serve  as 
reduits.  They  are  connected  with  the  central  reduit  by 
loop-holed  walls. 

624... The  covered-ways  are  without  traverses.  A  case- 
mated  reduit  or  traverse  separates  the  re-entering  places  of 
arms,  on  each  side,  from  the  covered-ways  of  the  enceinte 
and  inde[tendent  work,  and  sweeps  them  both.  These  are 
connected  by  looi)-holed  walls  in  front,  which  join  those  in 
their  rear. 

625... The  counterscarps  of  the  enceinte  and  independent 
work  are  of  earth. 

626... A  passage  leads  from  the  interior  across  the  main 
•litch  on  each  side  of  the  central  casemated  edifice,  and 
extends  ahnig  the  counterscarp  of  the  enceinte.  This  {pas- 
sage is  a  few  feet  above  tlie  water  level,  the  two  ends  being 


198  Wn]{K    AT    (iERMERSriKIM. 

connected  bv  bridges  across  tliat  portion  of  tlic  ni:iiii  ditch 
where  the  arched  conininnication  under  the  nuiin  caiion- 
niere  is  placed.  This  ])assagc  is  swept  by  two  small, 
caseniated  caponnieres,  which  project  from  the  sides  of  the 
main  caponniere. 

627... Ramps  lead  from  the  level  of  this  passage  to  the 
interior  of  the  independent  work  at  its  gorge,  and  to  that 
of  the  re-entering  places  of  arms. 

G2S...An  interior  and  exterior  system  of  mines  is  con- 
nected with  the  independent  work  and  the  r6dnits  of  the 
re-entering  place  of  arms. 

629. ..In  the  application  of  this  sj'stem  to  wet  ditches,  the 
means  of  communication  between  the  enceinte  and  the 
various  outworks,  by  the  passages  and  small  bridges,  across 
the  main  ditch  and  along  the  sides  of  the  central  capon- 
niere, are  principally  noticeable,  as  the  other  features  do 
not  differ  in  any  great  degree  from  its  application  to  dry 
ditches.  Here  one  of  the  main  objections  to  wet  ditches, 
the  difficulty  of  keeping  open  a  communication  hy  means 
of  rafts  or  boats,  for  sorties  and  other  purposes,  is  obviated 
by  the  arrangement  of  the  passage  in  question.  The 
bridges,  connecting  the  break  in  this  passage,  ma}'  be  so 
arranged  as  to  be  readily  removed  or  destroyed  when  the 
besieger  has  gained  such  a  footing  beyond  the  main  ditch 
as,  by  a  rapid  assault,  to  endanger  the  safety  of  the  enceinte. 
This  mode,  however,  of  establishing  a  foot  communication 
between  the  enceinte  and  the  outworks  of  a  front,  is  not 
peculiar  to  this  system;  as  like  means  are  used  in  the 
bastioned  system,  by  placing  the  bottom  of  the  double 
caponniere  slightly  above  the  water  level  of  the  main  ditch, 
connecting  the  two  parts  of  this  ditch,  on  each  side  of  the 
caponniere,  by  a  narrow  ditch,  between  this  and  the  gorge 
of  the  demilune  redoubt,  over  which  a  slight  temporary 
bridge  is  thrown,  so  long  as  it  is  found  necessary  to  keep 
open  this  communication. 

680... The  German  engineers  apply  the  preceding  dispo- 
sitions to  every  class  of  detached  works,  Avhether  within 
reach  of  the   artillery  of  the  main  work  or  beyond  it.     In 


WORK    AT    GERMERSIIEIM.  199 

tlie  former  case,  the  work  is  either  in  the  form  of  a  lunette 
or  a  redan,  according  to  the  requirements  of  the  site,  tlie 
gorge  of  tlie  work  heing  secured  hy  a  slight,  loop-holed 
wall  that  can  he  readily  destroyed  by  the  artillery  of  the 
place,  and  thus  open  its  interior  to  view  when  occupied  hy 
the  besieger.  In  the  latter,  the  plan  is  that  of  a  polygonal 
redoubt  enclosed  on  all  sides  by  a  parapet.  The  ditches  in 
all  such  cases  are  flanked  by  small  caponniorcs,  placed  at 
the  angles  of  the  work,  and  arranged  both  for  musketry 
and  artillery,  besides  a  counterscarp  gallery,  which  serves 
as  the  point  of  departure  for  the  galleries  of  the  exterior 
system  of  mines. 

631... Remarks.  The  apparently  wide  divergence  be- 
tween the  German  fortification  of  the  present  day  and  the 
bastioned  system,  which  last  had  been  adopted  as  the  nor- 
mal one  throughout  tlie  world  until  these  innovations  were 
})ractically  introduced,  has  given  rise  to  active  discussions 
among  engineers  in  Europe,  in  which,  as  in  all  such  cases, 
very  ultra  ground  has  been  taken  by  both  parties  to  the 
dispute.  In  each  system  the  points  admitted  as  essential 
in  all  fortification  of  a  permanent  character  are  sought  for, 
viz:  1st,  an  enceinte  secure  from  escalade  and  thoroughly 
flanked  by  artillery  and  small  arms;  2d,  such  an  adaptation 
of  the  plan  of  the  enceinte  to  the  site  as  shall  secure,  as 
far  as  practicable,  the  principal  lines  from  enfilading  views; 
3d,  outworks  of  sufficient  strength  in  themselves,  and  of 
such  defensive  relations  to  the  enceinte,  as  to  force  the 
besieger  to  carry  them  b}'  regular  approaches  before  being 
able  to  assault  the  enceinte;  4th,  interior  defensive  works, 
or  keeps  within  the  assailable  points  of  the  enceinte,  and 
in  the  outworks  first  subject  to  an  attack,  to  give  confidence 
to  their  garrisons  in  holding  out  to  the  last  extremity;  5th, 
the  means  necessary  for  an  active  defence;  6th,  the  use  of 
mines  as  an  auxiliary  ;  7th,  tlie  protection  of  all  masonry 
bv  earthen  masks  from  the  distant  batteries  of  the  besicirer. 

632. ..The  only  (juestion  then  is,  by  which  of  these  two 
systems  the  object  in  view  is  best  attained.  In  the  solution 
of  this  question,  we  arc  met  at  the  out-set  by  the  absence  of 


^•- 


200  -WOUK    AT    GERMERSIIEIM. 

any  reliable  tests  as  to  the  real  value  of  the  defensive  means 
adopted  in  the  German  system.  No  place  fortified  by  this 
mode  has  yet  been  subjected  to  a  siege,  and  nothing  can, 
therefore,  be  with  certainty  stated  as  to  the  degree  of  resist- 
ance the  peculiar  defensive  means  adopted  may  be  expected 
to  aftbrd,  except  some  experiments  made  at  Woolwich, 
England,  some  years  ago,  to  test  the  practicability  of 
breaching  detached  scarps,  like  those  of  Carnot,  Avheii  cov- 
ered by  an  earthen  mask,  with  heavy  guns  throwing  their 
projectiles,  within  the  usual  range  of  ricochet  tire,  over  the 
earthen  mask  to  reach  the  wall  covered  by  it;  and  others 
made  at  Bapaume,  France,  on  the  effects  of  shot  on  defen- 
sive casemates.  These  experiments,  together  with  some 
facts  drawn  from  the  sieges  in  Italy  and  Spain,  during  the 
period  between  the  first  French  revolution  and.  the  peace 
of  1815,  and  the  more  recent  attacks  on  fortifications  during 
the  struggle  between  Kussia  and  the  Allies,  go  to  show 
that  all  structures  of  masonry,  whenever  they  can  be 
reached  by  heav}-  projectiles  within  the  range  of  800  to 
1,000  yards,  whether  in  view  or  not,  may  be  greatly  dam- 
aged if  not  entirely  ruined  ;  and  that  troops  within  defen- 
sive casemates  exposed  to  such  a  fire,  would  be  soon  driven 
out  of  them  by  the  embrasure  shots,  and  the  cannon  de- 
stroyed. That  the  flanking  caponnieres  of  the  enceinte 
and  of  the  independent  works  in  the  German  systems 
are  thus  exposed  and  liable  to  these  objections,  does  not 
admit  of  a  question.  Like  assertions  may  be  made  of  the 
scarps,  which  are  either  wholly  or  partly  detached,  and  of 
the  traverse  walls  by  which  the  corridors  of  the  enceinte 
are  divided  for  defence.  The  defensive  barracks  in  the 
gorges  of  the  independent  works,  and  which  serve  as  their 
I'cduits,  as  well  as  the  loop-holed  wall  by  which  the  gorges 
of  these  works  are  closed,  being  thrown  back  from  the 
cover  of  their  parapets,  are  also  similarly  exposed.  The 
German  engineers,  it  is  said,  have,  by  the  dispositions 
made  in  some  of  their  more  recent  structures,  by  abandon- 
ing the  countersloping  glacis  of  Carnot  and  his  detached 
scarps,  employing  in  their  stead,  on  fronts  of  attack,  scarps 


.^ 


WORK    AT    GERMERSIIEIM.  201 

with  relievino;  arches,  and  covering,  to  some  extent,  their 
ditcli  caponniere  defences  hy  earthen  masks,  shown  some 
distrust  of  the  methods  mostly  used  in  their  first  structures, 
planned  upon  the  views  of  Montalemhert  and  Carnot. 

633. ..The  polyognal  tra^e,  which  obtains  in  most  of  the 
recent  German  works,  has  certain  prominent  advantages 
and  defects  which  may  1)C  seen  by  a  slight  comparison 
with  the  bastioned  system.  As  the  exterior  sides  are  longer, 
and  the  re-enterings  of  the  enceinte  less  deep  than  in  the 
bastioned  systems,  it  follows:  1st,  that  the  interior  space 
enclosed  by  the  enceinte  is  greater  in  the  polygonal  tra(;e ; 
2d,  that  the  faces  of  the  enceinte  are  less  exposed  to  rico- 
chet from  the  greater  obtuseness  of  the  salient  angles ;  3d, 
that  the  fire  of  the  faces  have  thus  a  better  bearing  on  the 
distant  defence;  4th,  that,  requiring  fewer  fronts  on  a  given 
extent  of  line  to  be  fortified,  there  will  be  fewer  flanks  and 
more  artillery,  therefore,  disposable  for  the  faces  and  cur- 
tains; 5th,  that,  in  the  usual  mode  of  attack,  the  besiegers 
will  l)e  forced  into  a  greater  development  of  trenches  for 
the  same  number  of  fronts.  Such  arc  the  advantages  in- 
herent in  this  trac^e. 

634. ..Its  defects  are:  1st,  that  the  enceinte  having  no 
other  flanking  defence  than  the  main  caponniere,  it  will  be 
exposed  to  an  escalade  so  soon  as  the  fire  of  this  defence  is 
silenced  ;  2d,  that  the  progress  of  the  besiegers,  during 
the  last  and  most  important  period  of  the  siege,  is  but  little 
delayed,  owing  to  the  slighter  re-enterings  formed  by  the 
independent  works  in  front  of  the  enceinte  salients. 

635... The  defects  in  the  bastioned  tra^e,  and  the  modes 
proposed  by  difterent  engineers  to  remedy  them,  particu- 
larly those  of  Ilaxo  and  Choumara,  have  been  sufficiently 
dwelt  upon  to  show  that,  with  the  advantages  inherent 
in  this  trac;e  of  preserving  tlie  means  of  flanking  the  en- 
ceinte ditch  to  the  last,  of  throwing  the  bastion  salients 
into  deep  re-enterings,  and  giving  a  better  direction  to  the 
enceinte  faces  for  sweeping  the  ground  in  advance  of  the 
demilune  salients,  it  is  susceptible  of  receiving  all  the 
means  of  casemated  defences,  of  a  great  development  of 


202  CKUMAX    FORTS. 

flank  lii'o,  of  driViisivc  arraiigcnionts  of  mines,  of  aniplo 
coniniunirations  for  an  active  defence,  and  an  extension  of 
tlie  exterior  side,  fortitied  commensurate  Avitli  the  improve- 
ments of  late  years  in  artillery  anti  small  arms. 

G3(3...In  the  discussions  whicli  have  taken  place  upon  the 
merits  of  tliese  two  traces  between  engineers  of  the  two 
rival  schools,  each  has  seemed  dis[)osed  to  exaggerate  tlie 
defects  and  to  depreciate  the  advantages  of  the  system 
anal3'zcd,  and  has  conducted  his  mode  of  attack  aecording- 
1}'.  Tlie  true  point,  however,  as  to  the  inherent  merits  of 
tlie  question,  does  not  lie  in  a  comparisoL  of  the  means  of 
resistance  of  a  bastioned  tra^e,  with  defective  communica- 
tions and  without  casematcd  defences  and  mines,  and  that 
of  the  German  system,  but  between  the  former,  with  these 
additions,  now  regarded  bj  engineers  of  every  school  as 
indispensable  to  a  vigorous  defence  against  the  greatly  im- 
proved means  of  attack  of  the  present  day,  and  the  latter. 

637. ..The  fragility  of  masonry,  and  the  ease  with  which 
it  can  be  ruined  by  distant  battei'ies  of  heavy  calibre,  par- 
ticularly when  pierced  with  embrasures  and  loop-holes,  like 
the  casemated  caponnieres  and  defensive  barracks  of  the 
German  system,  must  naturally  incline  engineers  to  limit 
its  employment  as  much  as  possible,  reserving  its  use  for 
positions  where  it  will  not  be  subject  to  this  exposure,  or 
where  it  can  be  so  covered  with  an  eui-then  mask  that  noth- 
ing may  be  a]»prehended  from  the  besieger's  heavy  guns. 


iii^rmHii  Sm^i^, 


638... In  their  detached  works,  or  isolated  forts,  the  Ger- 
man engineers  follow  the  same  defensive  measures  as  in 
the  inde[)endent  works  belonging  to  a  continuous  enceinte. 
A  strong,  casemated   barrack,  PI.  33,  Fig.  2,  the  plan  of 


GERMAN    FORTS.  203 

wliieli  is  either  cnrvilinear  or  polygonal,  with  several  tiers 
of  fire,  serves  as  the  rediiit  or  keep  of  the  work,  and  is 
placed  either  witliin  it  or  at  its  gorge,  according  to  the 
position  to  be  occupied.  The  interior  is  provided  with 
casemates  for  guns  and  mortars,  placed  at  the  salients  and 
along  the  terreplein  —  frequently  under  traverses,  when 
these  are  used  to  cover  a  face  from  enfilading  views.  The 
scarp  walls  are  usually  built  with  relieving  arches,  defensive 
scarp  galleries,  and  open  corridors  behind  the  upper  part  of 
the  scarp  wall,  which  is  also  loop-holed.  The  ditches  are 
flanked  by  small  caponniercs,  placed  at  the  angles  of  the 
"w^ork,  or  along  its  faces,  and  by  loop-holed  counterscarp 
galleries;  and  mines  for  exterior  and  interior  defence  are 
connected  with  these  galleries  and  with  the  ditch  which 
usually  surrounds  the  keep. 

639. ..Tower  Forts.  The  favor  with  which  the  views  of 
jVfontalembert  have  been  received  in  Germany,  has  led  to 
the  adoption  of  his  circular  casemated  towers,  both  as  iso- 
lated forts  and  combined  iu  a  system  of  detached  works  for 
covering  a  space  to  their  rear  for  an  entrenched  camp,  as  at 
Lintz.  These  towers,  in  their  interior  arrangements,  are 
the  same  as  the  defensive  barrack  already  described,  with 
the  exception  of  those  difterencej  in  the  details  of  the  con- 
struction which  the  dift'erence  in  their  plans  would  call  for. 
They  have  several  tiers  of  covered  fire  for  artillery  and 
musketry,  and  an  open  battery  on  top,  the  parapet  of  which 
is  either  of  earth  or  of  masonry,  according  to  the  dimen- 
sions of  the  tower.  In  the  towers  at  Lintz  they  are  sur- 
rounded by  a  ditch,  and  the  whole  of  the  masonry  which 
would  be  exposed  to  the  besieger's  batteries  is  covered  by 
a  glacis,  leaving  only  the  guns  on  top  to  have  direct  views 
on  these  batteries,  the  second  tier  firing  under  an  elevation 
over  the  crest  of  the  glacis  mask.  Tiie  ditch  toward  the 
interior  is  crossed  by  a  temporary  fixed  and  a  drawbridge 
leading  to  the  second  story  of  the  tower.  The  guns  of  the 
top  battery  are  placed  on  a  revolving,  platform,  their  car- 
riages l)eing  of  a  peculiar  construction,  to  admit  of  the 
axes  of  the  guns  remaining  parallel,  so  as  not  to  liave  their 


20 i  THE  ADAPTATION  OF  PERMANENT  FORTIFICATION 

shot  diverge  from  the  object  to  be  reached,  and,  at  the  same 
time,  to  occupy  as  little  space,  laterally,  as  will  just  suffice 
for  the  service  of  the  guns.  An  earthen  parapet  covers 
the  guns  on  the  side  exposed  to  the  besieger's  fire,  and  one 
of  masonry  toward  the  interior.  These  towers,  with  the 
exception  of  the  open  battery,  have  the  defects  of  diverg- 
ent fires,  common  to  all  works  with  a  circular  plan  ;  and 
the  oj)cn  battery  is  liable  to  be  rendered  useless,  or  be 
ruined  bv  a  well-aimed  shot  or  two,  or  a  heavv  shell  falling 
on  its  platform.  The  tower  without  earthen  masks  can 
only  be  used  with  advantage  in  positions  where  it  will  not 
be  exposed  to  being  breached  from  a  distance,  and  is  a  very 
good  auxiliary  in  sea-coast  defence,  for  points  where  the 
object  is  solely  to  prevent  an  enemy's  vessels  from  making 
use  of  a  safe  anchorage  on  the  coast. 


®he  ^dnplalion  of  |3crm;inrnt  Jforfijiciition  to  the 
Sopographital  cjcaturcfi  of  (J;rontierfi. 


640. ..No  state,  in  the  present  condition  of  civilization, 
can  be  regarded  as  secure  from  foreign  military  aggression, 
the  accessible  points  of  whose  frontiers  are  not  occupied 
by  permanent  fortifications  of  such  strength  as  shall  pre- 
vent an  enemy  from  obtaining  possession  of  them  by  a 
sudden  assault,  and  thus  procuring  the  means  of  penetrat- 
ing into  the  interior.  Guided  by  the  experience  of  centu- 
ries of  wars,  and  the  daily  increasing  facilities  which  the 
improvements  in  the  materiel  of  armies  and  their  transpor- 
tation atlbrd  for  rapid  and  powerful  offensive  operations,  the 
ruling  states  of  continental  Europe  have,  within  the  last 
quarter  of  a  century,  not  only  made  every  effort  to  place 
their  frontiers  in  an  unassailable  condition,  but  also  their 


TO  THE  TOPOGRAPHICAL  FEATURES  OF  FRONTIERS.         205 

great  centres  of  population  and  wealth  in  the  iiitcrior,  he- 
yond  the  chances  of  a  sudden  attack  from  an  enemy  who 
might  force  his  way  through  the  frontier  defences,  and 
march  rapidly  upon  them,  thus  making  these  positions 
the  rallying-points  where  a  defeated  army  can  find  a  safe 
resting-place,  until  it  can  he  reorganized  and  sufficiently 
strengthened  to  resume  the  offensive.  Such  seems  to  he 
the  result  at  Avhich  the  generals  and  statesmen  of  Europe 
have  arrived,  after  the  most  mature  and  careful  considera- 
tion of  the  important  problem  of  national  defence,  during 
which  the  utility  of  permanent  fortifications  was  seriously 
called  in  question  by  some  who  pointed,  in  support  of  their 
views,  to  the  very  inefficient  part  the  great  numl)cr  of  for- 
tified places  had  played  in  the  wars  waged  by  ISTapoleon, 
when,  by  means  of  overwhelming  numbers,  he  was  enabled 
to  disregard  such  places,  the  garrisons  of  which  were  too 
feeble  to  make  any  efficient  offensive  movements,  until  the 
defeat  of  his  adversary,  in  one  or  more  great  pitched  bat- 
tles, necessarily  also  threw  them  into  his  possession. 

641... In  view  of  the  arguments  based  on  these  events, 
the  opinio!is  of  ISTapoleon  himself  should  carry  great  weight. 
In  speaking  of  the  bearing  of  permanent  fortifications  in  a 
defensive  war,  he  says:  "If  fortresses  can  neither  secure  a 
victory  nor  arrest  the  progress  of  a  conquering  enemy,  they 
can  at  least  retard  it,  and  thus  give  to  the  defensive  the 
means  of  gaining  time,  a  most  important  advantage  in  all 
warfare."  In  like  manner,  the  Archduke  Charles,  of  Aus- 
tria, who  showed  himself  one  of  the  ablest  adversaries  with 
whom  Napoleon  had  to  cope,  takes  the  ground:  "That  a 
defensive  warfare  cannot  be  systematically  and  successfully 
carried  on  in  a  country  which  is  not  provided  with  fortresses 
that  have  been  planned  and  distributed  according  to  strate- 
gical requirements."  Like  views  were  held  by  the  Duke  of 
Wellington,  and  it  is  probable  that  no  great  general,  from 
the  earliest  period  of  military  operations  down  to  the  pres- 
ent moment,  has  ever  entertained  the  contrary,  Without 
going  further  back  than  the  two  great  contests  which  have 
taken  place  in  Europe  within  the  last  few  years,  we  gather 


206  THE  ADAPTATION  OF  PERMANENT  FORTIFICATION 

the  strongest  testimony  to  the  soundness  of  these  views. 
AVe  find,  on  the  one  side,  the  efforts  of  powerful  Russian 
forces  paralyzed  by  the  obstinate  defence  of  a  few  weak 
fortresscr*,  and,  in  some  cases,  of  sini[>le  field-works  by  the 
Tniks;  on  the  other,  the  <;ia:aiitic  armaments,  by  sea  and 
land,  of  France  and  England  combined,  held  at  bay  in  the 
East,  and  in  tlie  Black  sea;  and,  more  lately,  the  career  of 
France  arrested  in  the  very  flush  of  victory,  by  the  time 
which  it  must  necessarily  have  cost  her  to  break  down  the 
barriers  which  Austria  had  placed  in  her  way  in  the  strong- 
holds of  Xorthern  Italy.  The  only  question,  then,  on  this 
subject  that  remains  for  solution  by  a  state  is  in  what  way 
such  a  means  of  security  from  aggression  can  be  best  adapt- 
ed to  its  own  geographical,  political  and  military  status. 

(342. ..In  a  country  like  our  own,  with  so  vast  an  extent 
of  sea-coast  and  inland  fi-ontier,  and  with  political  and  social 
institutions  which  are  so  antagonistic  to  every  approach  to 
the  maintenance  of  a  large  standing  army  as  a  measure  of 
national  safety,  this  question  is  one  of  peculiar  importance, 
both  from  the  open  character  of  this  extensive  frontier,  and 
from  the  almost  incredible  facility  with  which,  as  in  the  late 
struggles  in  Europe,  and  in  the  contests  of  China  and  India, 
considerable  armies,  with  all  their  materiel^  can  be  concen- 
trated on  distant  points  by  the  aid  of  steam. 

643. ..The  want  of  military  means  of  some  of  our  imme- 
diate neighbors,  and  the  daily  increasing  mutual  commer- 
cial interests  between  us  and  the  greatest  naval  power  of 
the  world,  from  whom  alone  we  have  any  serious  danger  to 
ai)iirehcnd  ah)ng  our  inland  frontier,  would  seem  to  favor 
the  liojie  tliat  the  day  may  never  arrive  in  which  our  coun- 
try will  have  to  provide  against  invasion  except  along  the 
sea-coast;  and  we  may,  therefore,  dismiss  from  our  consid- 
eration any  further  provision  against  this  eventuality  than 
the  security  of  our  principal  harbors,  naval  stations  and 
commercial  marts  from  a  naval  attack,  or  from  one  com- 
bined with  the  descent  of  a  land  force,  which  last,  from  the 
great  resources  of  our  country  in  men  and  means,  would 
hardly  attempt  to  penetrate  inland  beyond  one  or  two 
marches. 


TO  THE  TOPOCrvAPIirCAL  FEATURES  OF  FRONTIERS.  207 

G44...Tn  the  organization  of  the  frontier  fortiiications  of  a 
state,  tlie  points  to  be  chiefly  regarded  are  the  principal 
avennes  of  access  to  tlie  interior,  and  the  topographical 
features  of  the  frontiers,  as  they  lend  themselves,  more  or 
less,  to  strengthen  artificial  defences.  In  conducting  an  in- 
vasion across  an  inland  frontier,  the  march  of  the  enemy 
must  necessarily  be  along  the  roads  that  intersect  it,  as 
these  aftbrd  the  only  good  avenues  for  transporting  the 
materiel,  etc.,  of  the  arni}'.  The  })oints,  therefore,  or  places 
in  their  neighborhood,  where  the  principal  roads  or  other 
avenues  of  communication  cross  the  frontier,  particularly 
those  Avhich  lead  to  the  great  centres  of  population  and 
wealth,  are  the  ones  which  necessarily  require  pernuuient 
defences.  Xo  absolute  rule  can  be  laid  down  for  the  dis- 
tribution or  the  strength  of  such  works.  Everything  must 
depend  upon  the  more  or  less  of  facility  presented  to  an 
enemy  for  penetrating  at  one  point  rather  than  another, 
and  of  the  ulterior  advantages  which  the  possession  of  one 
may  present  to  him  over  another. 

645. ..Rivers  and  mountain  ranges  are  the  natural  fortifi- 
cations of  states,  and,  where  they  form  the  frontiers,  they 
greatly  facilitate  the  application  of  artificial  defensive 
means,  as  they  present  but  few,  and  those,  in  general, 
important  points  of  access.  When  the  points  of  commu- 
nication on  a  river  are  fortified,  an  invading  force,  however 
powerful,  cannot,  without  great  risk,  cross  the  river  before 
first  gaining  possession  of  them  ;  for,  even  should  a  sufiici- 
ent  detachment  be  left  to  observe  and  blockade  the  for- 
tresses, the  main  army,  in  case  of  retreat  or  any  disaster, 
might  be  placed  in  an  extremely  critical  position,  in  its 
movements  to  recross  the  river,  with  the  garrisons  of  tlie 
fortresses  threatening  its  flanks  and  rear.  In  ofixuisive 
operations,  fortresses  upon  a  river  frontier  form  one  of  the 
strongest  bases  of  ojierations  for  an  arnn*.  If  a  river  inter- 
sects the  fi'ontici-,  the  point  wlui-e  it  crosses  it,  or  some  one 
in  its  vicinity,  should  be  occupied  by  a  permanent  work. 
Among  such  points,  those  arc  more  peculiarly  necessarv  to 
be  held  where  a  river,  forming  the  frontier,  is  intersected 


208  THE  ADAPTATION  OF  PERMANENT   FORTIFICATION 

by  another  navio^able    one  which    lie?;  wliolly   Avithiii    the 
frontier. 

64(5. ..With  resjicct  to  mountain  passes,  the  main  roads 
ah»n('  will  require  permanent  works.  If  the  passes  are  in- 
dependent of  each  other,  a  work  will  be  necessary  for  each 
one  separately' ;  but  where  several  unite  at  the  same  point, 
njion  or  within  the  frontier,  a  single  work,  placed  ujion  tins 
l»oint,  will  suffice.  Local  circumstances  will  determine  the 
point  in  each  pass  which,  occupied,  will  offer  the  greatest 
advantage  of  obstructing  the  march  of  an  invading  foi'ce. 
The  only  rule  that  can  be  given  is  that,  whilst  the  position 
selected  sliall  satisfy  this  condition,  there  shall  be  every 
facility  of  communication  between  the  fortress  and  the  in- 
terior for  receiving  supplies  and  reinforcements.  This  rule 
would  lead  generally  to  the  selection  of  some  point  of  the 
outlet  lying  within  the  frontier  as  the  proper  one. 

647. ..The  number  of  fine  natural  harbors  and  roadsteads 
on  our  seaboard,  wdiere  the  largest  fleets  can  find  a  secure 
anchorage  at  all  seasons;  the  proximitv  to  the  ocean  of 
many  of  our  most  important  cities,  towns  and  po})ulous  vil- 
lages, by  which  they  are  not  only  exposed  to  the  usual 
dangers  of  naval  attacks,  but  to  incursions  from  an  enemy's 
laud  forces;  together  with  the  large  riveis  whirh,  having 
their  outlets  on  this  seaboard  frontier,  are  navigable  for 
long  distances  within  it  by  vessels  of  the  greatest  burthen, 
have  given  to  the  subject  of  sea-coast  defences  a  particu- 
lar prominence  among  ourselves.  The  means  of  defence 
disposable  for  the  security  of  these  points,  consist  in  perma- 
nent works  arranged  to  meet  an  attack  both  by  sea  and  land, 
and  of  such  strength  as  the  })rcsumed  nature  of  the  attack 
will  demand  ;  of  such  temporary  fortiiications  as  the  exi- 
gency of  the  moment  may  point  out  ;  of  movable  land 
forces;  and  of  floating  defences  to  act  in  aid  of  the  others. 

648. ..The  character  of  the  permanent  defences  will  de- 
pend upon  the  object  in  view.  Where  this  is  simply  to 
exclude  an  enemy's  fleet  from  the  use  of  a  harbor,  or  road- 
stead, which  offers  to  him  no  other  inducement  for  its 
occupation  than  that  afforded  by  a  secure  anchorage,  one 


TO  THE  TOPOGRAPHICAL  FEATURES  OF  FRONTIERS.         209 

or  more  small  works  of  sufficient  strength  to  prevent  the 
success  of  an  open  assault  upon  them,  armed  with  heavy 
mortars  and  guns  with  long  ranges,  that  can  reach  by  their 
lire  every  point  where  an  enemy's  ship  could  safely  anchor, 
will  he  sufficient. 

649. ..The  points  to  be  occupied  l)y  these  works,  as  well 
as  their  plan,  will  depend  upon  the  natural  features  of  the 
harbor  or  roadstead.  They  will  usually  consist  either  of 
open  works,  armed  with  guns  in  barbette  and  mortars  that 
can  sweep  all  points  of  approach  to  and  within  the  harbor, 
or  of  a  combination  of  casemated  and  open  works.  Tiie 
gorge  of  the  works  in  all  cases  being  occupied  by  a  case- 
mated  tower,  of  sufficient  strength  and  capacity  to  hold 
a  garrison  of  sufficient  force  to  beat  off  an  open  assault 
on  the  battery  by  land,  and  be  itself  secure  from  a  coup  de 
main.  Like  defences  Avill  also  be  sufficient  for  the  security 
of  the  smaller  classes  of  towns  and  villages,  which  would 
])robably  offer  a  temptation  only  to  a  small  naval  force. 

650... In  the  case  of  important  commercial  cities  and 
large  naval  de[)ots  lying  within  harbors  more  or  less  acces- 
sible both  to  sea  and  land  attacks,  the  character  of  the 
defences  called  for  should  be  commensurate  with  the  maer- 
nitude  of  the  interests  to  be  guarded,  and  the  consequent 
temptation  to  an  enemy  to  put  forth  great  efforts  for  their 
occupation  and  destruction. 

651... The  avenues  of  approach  to  these  objects  by  sea, 
which  can  be  brouglit  within  range  of  cannon  and  mortars, 
in  fortifications  on  the  shore,  or  in  works  erected  on  natural 
or  artificial  islands,  should  be  occupied  to  a  distance  that 
will  prevent  a  fleet  from  approaching  near  enough  to  open 
a  boml)ardnK'nt;  and,  if  practicable,  should  also  force  the 
enemy,  if  he  ventures  a  land  attack,  to  disembark  his 
troops  cither  at  so  great  a  distance  from  the  object  to  be 
readied  that  he  will  not  be  able,  l»y  a  sudden  descent, 
to  eifect  a  surprise,  or  to  limit  his  landing  to  such  points 
on  the  coast  as,  from  their  exposed  position,  may  render 
the  co-operation  of  the  naval  and  land  forces  very  uncer- 
14 


210  Tin;  ADAPTATION  OF  PKRMANKNT  FORTIFrCATrON 

tain,  and,   in    cast'  of  a  stonn,   place   tin*  latter   in   a  very 
perilous  condition   if  attacked. 

r)r)2...The  exterior  chain  of  the  defences  will  consist  of 
works  of  the  above  character.  AVithin  these,  batteries, 
eitlier  open  or  casemated,  as  the  locality  may  seem  to 
demand,  should  occupy  all  the  most  suitable  positions  both 
for  sweeping  the  path  that  a  fleet  must  follow  l)y  jxiwcrful 
cross,  direct  and  enfllading  lires,  and  for  reaching  every 
point  of  anchorage  within  the  harbor.  On  the  land  ap- 
proaches, points  should  be  occupied  by  forts  of  a  permanent 
character,  which  will  prevent  a  sufHciently  near  approach 
to  bombard  the  city  or  depot,  and,  in  combination  with 
temporary  works,  altbrd  an  intrenched  field  of  battle  for 
the  troops  on  the  defensive.  These  will  form  the  exterior 
line  of  the  land  defences;  the  interior  line  being  eitlier 
a  continuous  enceinte  of  permanent  fortilication  whicli  will 
require  a  regular  siege  for  its  reduction,  or  else  a  suitable 
combination  of  either  continuous  or  detached  field-works 
of  such  strength  and  armament  that  the  enemy,  in  any 
attemi)t  to  carry  them  by  an  open  assault,  will  be  made 
to  suffer  heavily,  even  if  he  is  not  repulsed.  The  security 
of  objects  of  this  character  will  be  greatly  increased  when 
they  lie  at  some  distance  within  the  sea-coast  frontier,  and 
can  only  be  approached  either  l)y  water,  through  such  com- 
paratively narrow  detilcs  as  even  our  largest  rivers  present, 
or  by  land  only  after  one  or  more  marches.  These  defiles 
will,  for  the  most  part,  not  only  present  admirable  positions 
on  their  baid-cs  from  which  they  can  be  enfiladed  within  the 
range  of  the  heaviest  guns,  but  frequently  others,  at  points 
where  the  river  narrows,  or  changes  its  course,  where 
w^orks,  occupying  the  opposite  banks,  w'ill  give  the  means 
of  rendering  the  river  impassable  by  booms,  rafts  or  other 
floating  or  sunken  obstructions,  which  cannot  be  removed 
except  by  getting  i)Ossession  of  the  defences,  by  which  they 
are  guarded,  by  a  land  attack. 

G53... Wherever  harbors  or  bays  are  of  that  extent  that 
their  entrance  cannot  be  interdicted  to  an  enemy's  fleet, 
nor  secure  anchorage  within  them  be  prevented,  of  which 


#T0  THE  TOPOGRAPHICAL  FEATURES  OF  FRONTIERS.    211 

we  have  examples  on  our  coast,  the  case  falls  l)eyon(l  tlie 
province  of  fortitication  and  must  l)e  left  to  floatiiiLj;  de- 
fences for  a  solution.  Here  even  some  fortified  har1)ors  on 
the  shores  of  sucli  extensive  estuaries  may  give  secure 
places  of  refuge  for  sliips  of  war,  from  which  they  may  at 
any  moment  sally  Avhen  they  can  take  the  enemy  at  disad- 
vantage, or  into  which  they  can  retreat  if  attacked  by  n 
su[»crior  force. 

Go4...The  necessity  of  fortitication s  for  the  security  of 
frontiers  being  admitted,  there  is  seldom  any  doubt  as  to 
the  points  to  be  occupied,  as  these  are  usually  unmis- 
takably marked  out  by  nature  herself  Of  the  character 
of  the  defences  for  these  points,  the  features  of  the  locality 
and  tlie  importance  of  the  points  themselves  to  military 
operations,  either  defensive  or  otfensive,  beyond  the  imme- 
diate range  of  their  guns,  must  decide.  Here  the  (piostion 
comes  exclusively  within  tbe  donuiin  of  the  engineer,  and 
its  solution  will  be  more  or  less  perfect  as  he  has  the  abilitv 
to  adapt,  in  the  best  manner,  all  the  resources  of  his  art  to 
the  peculiar  circumstances  of  the  case  before  him. 

655. ..In  the  powerful  military  states  of  continental  Eu- 
rope, the  fpiestion,  as  to  what  extent  the  great  centres  of 
poimlation  and  wealth  in  tlic  interior  should  be  covered  bv 
fortitications,  has  l)een  submitted  to  the  investigation  of 
tlie  ablest  engineers  and  statesmen,  from  the  time  of  Van- 
ban  down  to  the  present  day,  but  moiv  ]»articularly  since 
tbe  fall  of  Xapoleon,  a  catastrophe  which  might  not  have 
taken  place  had  Paris  been  secured  by  fortifications,  which 
would  have  prevented  a  coup  dc  main  when  the  armies  of 
tlie  Allies  gained  jM)ssession  of  it  as  the  result  of  a  pitched 
battle.  Whatever  differences  of  opinion  have  been  called 
forth,  as  to  the  mode  of  accomplishing  this  object,  as  shown 
in  the  published  views  on  the  proposition  to  fortify  Paris, 
there  seems  Xo  have  been  none,  among  those  best  qualified 
to  decide  upon  it,  as  to  the  great  importance  of  so  fortifv- 
ing  tliis  capital,  and  otli^r  large  places  in  the  interior,  as 
Lyons,  etc.,  whicli,  from  tlieir  position,  must  be  of  the  lii<;h- 
est  strategical  value,  in  tlie  case  of  a  successful  invasion  l)v 


212  ADAPTATION  OF  PERMANENT  FORTIFICATrON. 

a  largo  army,  as  not  only  to  jirovcnt  tlioir  wealth  and  ro- 
sourcos  from  falling  into  the  possession  ot  the  invading 
force,  but  to  make  them  safe  rallying-points  for  beaten  and 
dispersed  forces,  and  de[)6ts  for  organizing  new  armies. 
Tlie  plan  that  has  been  adopted  for  this  end  both  in  France 
and  in  most  of  the  other  parts  of  Europe,  which  have  been 
either  newly  fortified  or  had  their  old  works  strengthened 
within  this  period,  is  to  surround  the  city  by  a  continuous 
enceinte  of  greater  or  less  strength,  but  one  secure  from  a 
coup  de  main;  and  to  occupy,  with  forts  of  a  permanent 
character,  the  most  suitable  points  in  advance  of  the  en- 
ceinte, to  })revent  an  enemy  from  bombarding  the  city,  or 
peneti'ating  between  the  forts  without  iirst  gaining  posses- 
sion of  them.  By  this  plan,  it  is  i)roposed  to  gain  all  the 
advantages  oifered  by  the  passive  resistance  of  fortifications, 
and  the  activity  of  a  disposable,  movable  force  occupying 
the  zone  between  the  enceinte  and  the  forts  as  an  intrench- 
ed camp,  upon  which  the  forts  with  temporary  works  thrown 
up  between  them  would  render  an  open  assault  too  perilous 
to  be  attempted. 

656... The  enceinte  of  Paris  consists  of  continuous  bas- 
tioned  fronts  without  outworks,  having  a  revetted  scarp  of 
the  usual  height  to  secure  it  from  escalade,  and  a  ditch  with 
a  counterscai'p  of  earth.  The  advanced  forts  are  either 
quadrangular  or  pentagonal  bastioned  works,  enclosing  all 
the  means  of  security  for  their  garrisons,  as  bomb-proofs, 
etc.,  their  plan  being  skilfully  adapted  to  the  site,  and  to 
their  mutual  bearing  on  the  defence.  The  fortitications  of 
Lyons  present  more  diversity,  both  in  the  plan  and  details 
of  the  enceinte  and  forts,  although  the  general  system  is 
the  same  as  that  of  Paris.  In  the  last  is  seen  a  more  ex- 
tensive ai)plication  of  casemated  and  galler}-  defences,  both 
for  exterit)r  flanking  and  for  the  defence  of  the  interior  of 
tlie  forts:  growing  out  of  the  more  broken  features  of  the 
site  generally,  and  frequently  fi'om  the  more  confined  space 
occupied  by  them. 

657. ..In  Germany,  the  same  general  system  of  a  continu- 
ous enceinte,  with  strong  advanced  isolated  works,  has  been 


SUMMARY    OF    THE    PROGRESS    OF    FORTIFICATION.  213 

followed,  the  whole  being  planned  and  combined  according 
to  the  distinctive  featnrcs  of  what  is  known  as  the  Gorman 
system  of  fortification. 

658... In  our  own  country,  where  our  largest  centimes  of 
po])nIation  and  wealth  lie  almost  immediately  upon  the  sea- 
l)oard,  it  would  seem  imi)racticable,  in  view  of  the  rapid 
spread  of  }to})ulation  around  them,  and  the  consequent 
changes  in  local  features,  to  resort  to  any  defences  of  a 
permanent  character,  to  secure  them  from  a  land  attack, 
even  were  the  nation  willing  to  assume  the  burthen  of  the 
great  outlay  for  such  an  object,  as  in  a  few  ^^ears  the  works 
of  to-day  might  be  rendered  useless  b}^  the  changes  refer- 
red to.  Even  in  Europe,  the  strongest  despotic  govern- 
ments have  been  obliged  to  cede,  what  seemed  military 
exigencies,  to  the  dennmds  of  the  social  condition,  and 
either  to  raze  the  fortifications  of  cities,  to  give  room  to  a 
crowded  population,  or  else  to  suiier  such  encroachments 
on  the  ground  necessar}'  for  the  functions  of  the  works  as 
to  render  them  nearly  useless.  The  onl}-  defensive  resource 
that  seems  left  to  ourselves,  in  like  cases,  is  in  the  use  of 
field-works,  one  which  our  military  experience  shows  may 
be  relied  upon  with  confidence,  so  long  as  the  military  apti- 
tude of  our  po[)ulation  remains  unchanged,  from  what  it 
has  thus  far  been. 


s^ninmanj  af  the  prtifircfifi  of;  ^(ortificatiiin. 


^ 


6.39... The  records  of  history  and  the  vestiges  of  remote 
civilization  show  that  the  art  of  fortification,  in  some  guise 
or  another,  lias  been  in  practice  throughout  all  nations, 
even  in  the  lowest  stages  of  social  progress,  and  that,  wher- 
ever it  has  been  cultivated,  its  character  has  been  more  or 
less  infiuenced,  not  only  by  the  natural  features  of  the  coun- 
try, but  by  the  political  and  social  conditions  of  its  inbabi- 


l'14  PIMMARV    OF    THE    PROGRESS    OF    FORTIFICATIOX. 

tants.  In  its  earliest  applications,  we  find  men  resorting  to 
one  or  more  simple  enclosures  of  earthen  walls:  or  of  these 
surmounted  hy  stakes  placed  in  juxtaposition;  or  of  stakes 
alone  firmly  planted  in  the  ground  with  a  strong  wattling 
hetween  them;  or  of  timber  in  its  natuial  state,  having  its 
branches  and  the  undergrowth  strongly  interlaced  to  form 
an  impervious  obstruction,  with  tortuous  paths  through  it, 
known  onl}-  to  tlie  defenders. 

660... A  resort  to  such  feeble  means  shows  not  onh'  a 
ver}-  low  state  of  this  branch  of  the  military  art,  but  also 
of  that  of  the  attack,  as  defences  of  this  kind  would  pre- 
sent but  a  slight  obstacle,  except  against  an  enem}'  whose 
habitual  mode  of  warfare  was  as  cavalry,  or  of  one  not  3'et 
conversant  with  the  ordinary'  plans  for  scaling.  This  class 
of  fortifications  for  the  defence  of  entire  frontiers  has  been 
mostly  met  Avith  in  the  east  of  Europe,  and  was,  doubtless, 
at  the  time,  found  to  l)e  a  sufficient  protection  against  those 
nomadic  tribes  that  for  ages  have  roamed  over  its  vast 
plains,  and  who  are  only  formidable  as  a  mounted  force. 

661. ..The  next  obvious,  and,  in  humid  countries,  neces- 
sary step  was  to  form  walls  either  of  rough  blocks  of  stone 
alone,  or  of  these  interlaced  with  the  trunks  of  heavy  trees. 
Obstructions  of  this  kind  could  only  be  used  to  a  limited 
extent,  and  were  confined  to  the  defences  of  places  forming 
the  early  centres  of  population.  As  human  invention  was 
developed,  these,  in  their  turn,  were  found  to  present  no 
serious  obstacle  to  an  assault  by  escalade — giving  to  the 
assailed  only  the  temporary  advantage  of  a  more  command- 
ing [)osition — and  they  gave  place  to  walls  of  dressed  stone, 
or  l)rick,  whose  height  and  perpendicular  face  alike  bade 
defiance  to  individual  attempts  to  diinl)  them,  or  the  com- 
bined eiforts  of  an  escalade.  From  the  tops  of  tliese  inac- 
(;essil>le  heights,  sheltered  in  front  by  a  parapet  of  stone, 
and,  in  some  cases,  by  a  covered  corridor  behind  it,  the 
assailed  could  readily  keep  at  bay  any  enemy,  so  long  as 
he  could  be  attained  by  their  missiles;  but  having  reached 
the  foot  of  the  wall,  he  here  found  shelter  from  these,  and, 
by  procuring  any  cover  that  would  protect  him  from  ob- 


SUMMARY    OF    THE    PROGRESS    OF    FORTIFICATION.  215 

jects  thrown  from  above,  could  securely  work  at  cftecting  a 
breach  by  mining.  It  was  probably  to  remedy  this  detect 
of  simple  Avails  that  towers,  which,  at  first,  were  nothing 
more  than  square  or  semicircular  projections  built,  from 
distance  to  distance,  in  the  wall  itself,  were  first  devised. 
These,  subsequently,  wore  not  only  enclosed  throughout, 
but  divided  into  stories,  each  of  which  was  provided  with 
loop-holes,  to  ilank  the  adjacent  towers  and  the  straight 
portions  of  the  wall  between  them,  and  was  isolated  at  top 
from  the  straight  portion  of  the  walls  adjacent  to  it  by  a 
break  or  ditch,  on  the  interior,  between  the  tower  and  the 
wall,  across  which  a  communication  between  the  two  could 
be  established  by  a  temporary  bridge. 

662. ..These  formidable  defences  were,  in  their  turn, 
found  to  be  insufficient  against  the  ingenuity  and  skill  of 
the  assailant,  who,  by  means  of  covered  galleries  of  timber, 
sometimes  above  ground  and  sometimes  below,  gradually 
won  his  way  to  the  foot  of  the  wall,  where,  by  breaking 
his  wa}-  through  it,  or  by  undermining  and  supporting  it 
on  timber  props,  to  be  subsequently  destroyed  by  fire,  he 
removed  the  sole  obstruction  to  a  bodily  collision  with  the 
assailed.  In  addition  to  these  means  the  besiegers,  in  some 
cases,  resorted  to  the  use  of  lofty  wooden  towers,  wdiich 
were  covered  by  raw  hides  to  protect  them  from  fire,  from 
within  which  an  incessant  shower  of  arrows  and  other  mis- 
siles was  directed  against  the  assailed.  These  ponderous 
engines  were  gradually  moved  toward  the  walls,  on  in- 
clined planes  of  earth,  erected  with  incredible  toil,  to  give 
the  assailants  a  commanding  position,  and  to  enable  them, 
when  the  tower  was  brought  sufficiently  near  to  the  wall  to 
lower  a  drawljridgc  from  it,  to  bridge  the  cliasm,  and  bring 
on  a  hand-to-hand  contest  with  the  assailed. 

663... These  methods  of  attack  led  to  new  modifications 
in  the  defence,  which  consisted  in  surrounding  the  place  by 
wide  and  deep  ditches,  of  which  the  walls  formed  the 
scarp — the  counterscarp  being  either  of  earth  or  revetted 
with  stone.  This  placed  a  formidable  obstacle  to  the  mode 
of  attack  by  mining,   as  well   as  to   the    use   of  earthen 


216  SUMMARY    OF   THE    PROGRESS    OF    FORTIFICATION. 

niouiuls,  as  tljese  last  liad  to  be  erected  across  the  ditch 
before  suflicieiit  proximity  to  the  wall  could  he  gained, 
either  to  form  a  communication  with  its  top,  or  to  plant 
the  battering  ram — a  heavy  beam,  with  an  iron  or  brass 
liead,  Avhich,  swung  horizontally  within  a  wooden  tower, 
could  be  driven  by  men  with  sulhcient  force  to  breach  the 
lieaviest  Avails.  The  ditches,  also,  were  filled  with  water 
whenever  tliis  obstruction  could  be  procured.  AVhcii  dry, 
they  formed  a  defile  through  which  the  assailed  often 
sallied  upon  the  assailant  with  success. 

664... The  gigantic  proportions  often  given  to  the  fortifi- 
cations of  antiquit}',  as  well  as  their  extent,  seem  almost 
incredible  in  tlie  present  day.  In  many  cases  a  double 
wall  of  stone  or  brick  was  filled  in  between  with  earth, 
forming  a  wide  rampart  upon  wliich  several  vehicles  could 
go  abreast.  I^ot  only  Avas  the  space  enclosed  Avithin  the 
Avails  sufticient  for  the  habitations,  but  ground  enough  was 
said  to  be  taken  in,  also,  for  agriculture,  so  as  to  add  consid- 
erably to  the  food  of  the  inlial)itants  and  cattle,  for  the 
long  periods  to  Avhich  blockades  Avere  in  many  cases  ex- 
tended, Avhen  the  besiegers  had  failed  in  all  other  means  of 
reducing  the  place. 

665... The  Aval)  Iniilt  l)y  the  Eomans  in  Britain,  between 
Carlisle  and  Newcastle,  to  restrain  the  incursions  of  the 
]*icts  into  the  southern  portions  of  the  island,  Avas  sixteen 
miles  in  extent,  about  twelve  feet  in  height,  and  nine  feet 
in  thickness.  The  extent  and  dimensions  of  tliis  woi'k  sink 
almost  into  insignificance  when  compared  Avith  those  of  the 
celebrated  Avail  of  China,  built  to  restrain  the  incursions  of 
the  Tartars.  This  structure  is  about  1,500  English  miles  in 
length,  has  a  height  of  27  feet,  its  thickness  at  top  being  14 
feet.  The  lower  portion  of  it  is  built  of  dressed  stone,  the 
upper  of  Avcll  burned  brick.  It  is  flanked  at  distances  of 
about  80  yards  apart  by  towers,  iji  Avhich  iron  cannon  are 
found.  In  the  great  extent  it  embraces,  it  necessarily 
crosses  hills  and  A'alleys,  and  in  many  places  important 
defiles.  An  examination  of  its  parts  has  shoAvn  that  in 
its  [)lan  there  Avas  an  evident  design  to  adapt  it  to  those 


SUMMARY    OF    THE    PROGRESS    OF    FORTIFICATION.  217 

features  of  its  site,  as  it  is  well  thrown  back  to  the  rear, 
of  difliciilt  passes ;  and,  at  points  where  there  is  most 
danger  to  be  apprehended  from  invasion,  there  are  several 
walls  in  succession. 

666... The  mode  of  attack  of  fortified  places  resorted  to 
by  the  ancients,  was  reduced  to  settled  rules  and  brouglit 
to  the  highest  state  of  perfection  by  the  Greeks,  about 
the  epoch  of  Alexander  the  Great,  and  the  immediate  suc- 
cessors to  his  vast  conquests.  An  essential  ieaturc  in  it, 
whether  in  the  sieges  of  inland  fortresses  or  of  those  on  the 
seaboard,  was  to  cut  off  all  communication  between  the 
place  and  the  exterior,  by  hemming  it  in  b}'  sea  and  land ; 
with  stationary  forces,  covered,  themselves,  by  lines  of 
intrenchments  strengthened  by  towers,  and,  in  the  case  of 
sea-coast  places,  also  by  fleets.  The  besiegers  were  thus 
prepared  to  repel  all  assaults,  both  from  without  and  from 
the  invested  place.  Having  selected  the  portions  of  the 
place  0)1  which  the  main  attack  was  to  be  directed,  a  second 
line  was  formed  parallel  to  the  first,  which  was  covered, 
and  constructed  of  timber  and  wicker  work,  and  secured 
with  raw  hides  to  prevent  its  being  set  on  fire.  From  this 
sheltered  position,  which  served  also  the  purposes  of  a 
lodging  for  the  besiegers,  the  besieged  were  annoyed  with 
missiles  thrown  from  all  the  artillery  known  in  that  day, 
consisting  of  the  ordinary  bow,  the  cross-bow,  and  the 
various  machines  for  projecting  heavy  stones  and  other 
projectiles.  Under  the  diversion  thus  made,  the  besiegers 
pushed  forward  from  this  line  several  covered  approaches 
directly  upon  the  place,  for  the  purpose  of  gaining  the 
counterscarp,  and  IVoni  that  }>osition  filling  up  the  ditch 
Avith  stones,  earth,  heavy  bags,  etc.,  to  prepare  the  way  for 
placing  the  battcring-rain  in  jiosition  to  breach  the  wall. 
The  tower  in  which  this  machine  was  placed  usually  con- 
sisted of  several  stories,  and  was  occupied  In'  troops,  who 
cleared  the  top  of  the  wall  of  the  besieged.  This  operation 
was  frequently  aided  b}'  other  high  towers,  which  were 
advanced  either  on  the  natural  level  of  tlie  ground,  or  u[>on 


218  SUMMARY    OF   THE    PROGRESS    OF   FORTIFICATIOX. 

artificial  moniulr;,  forming  inclined  jtlanes,  so  that  any 
desirable  coninuuul  over  the  interior  conld  he  obtained. 

667. ..The  defence  was  mostly  of  a  passive  character:  the 
besieged  trusting  mainly  to  tiie  strength  of  their  defences, 
under  cover  of  which  they  resorted  to  all  the  means  used 
by  the  besiegers,  for  attaining  the  latter  when  they  came 
within  reach  of  their  missiles ;  using,  for  the  near  defence, 
cranes  and  other  devices  to  seize  upon  the  implements 
planted  at  the  foot  of  the  wall ;  and  constructing  galleries 
of  countermines  to  overwhelm  the  artificial  mounds  and 
their  towers. 

668... The  Romans  evinced  their  decided  military  apti- 
tude, not  only  in  the  employment  of  the  ordinary  system- 
atic methods  of  the  attack  and  defence  of  fortified  places, 
but  in  their  application  of  the  cardinal  principle  of  mutual 
defensive  relations  between  the  parts  of  a  fortified  position, 
obtained  by  advanced  and  retired  portions  of  the  enceinte ; 
and  also  in  the  adaptation  of  intrenchments  to  the  natural 
features  of  the  site,  as  shown  in  the  fortifications  of  some 
of  the  permanent  frontier  camps  of  their  military  colonies. 
The  application  of  these  principles  have  also  been  noticed 
in  some  of  the  fortified  pf)sitions  of  India,  which  consist  of 
a  mural  enceinte  with  earthen  ramparts,  flanked  b}'  round 
towers,  and  of  round  towers  in  advance  of  the  enceinte  and 
connected  with  it  by  caponnicrcs. 

669. ..With  the  decadence  of  the  Roman  empire,  the  art 
of  fortification,  like  the  other  branches  of  the  military  art, 
was  brought  to  so  low  a  stage  that  strongholds  which,  de- 
fended with  skill  and  energy,  would  have  bafiled  the  efi^brts 
of  a  well-trained  assailant  in  the  art  of  attack,  fell,  almost 
without  resistance,  into  the  possession  of  the  fierce  North- 
ern hordes  by  which  the  whole  of  civilized  Europe  was 
overrun.  The  remains  of  the  structures  raised  for  defensive 
purposes,  during  the  prosperous  days  of  the  empire,  were 
jirobably  the  sole  means  of  protection  afforded  to  the  in- 
habitants of  the  towns  that  still  maintained  a  nucleus  of 
population,  until  the  rise  of  the  Western  empire  under 
Charlemagne;    and  it  was  the  necessity  felt  by  this  con- 


SUMMARY    OF    THE    PROGRESS    OF    FORTIFICATION.  219 

qncror,  not  onl}^  of  securing  his  conquests,  but  of  checking 
the  irru[)tions  of  the  barbarous  tribes  ah)ng  his  extended 
frontier,  which  led  him  to  erect  tetes  dc  j^ont  on  the  frontier 
rivers,  and  a  line  of  strong  towers,  for  garrisons  of  a  few 
men,  upon  the  most  inaccessible  and  prominent  points  of 
this  frontier;  the  latter  being  a  means  which  was  subse- 
quently resorted  to  for  a  like  purpose  in  the  Spanish 
peninsula.  Henry  I,  of  Germany,  introduced  a  more  im- 
portant and  more  systematic  addition  to  these  permanent 
frontier  defences,  by  surrounding  the  frontier  towns  and 
villages,  occupied  by  military  colonists,  Avith  walls  and 
ditches,  to  secure  them  from  such  attacks  as  they  might  be 
exposed  to,  and,  subsequently,  by  adding  a  second  line  of 
strongholds  within  tlie  frontier,  by  which  an  irruption 
through  the  frontier  line  might  still  be  checked. 

670... During  the  general  disorganization  of  states  under 
the  feudal  system,  the  free  cities,  which  depended  for  their 
defence  on  the  burghers  composing  the  different  crafts, 
every  individual  who  could  maintain  a  few  retainers  in  his 
pay,  and  the  clergy  even  resorted  to  such  means  of  defence 
as  would  best  secure  them  from  the  attacks  of  otliers  in  a 
like  condition,  or  which  would  enable  them  to  carry  out 
that  system  of  pillage  that  had  become  general  amongst 
the  nobles  and  other  military  chieftains. 

671... From  this  state  of  society  sprung  up  those  castles, 
placed  in  the  most  inaccessible  positions  on  the  lines  of 
communication  which  the  little  inland  commerce  that  was 
still  carried  on  was  obliged  to  traverse.  These  castles 
were  provided  with  every  possible  device  for  an  obstinate 
passive  defence,  being  surrounded  by  a  wide  and  deep 
ditch,  or  moat,  over  which  a  drawbridge  was  the  only 
communication  to  the  main  entrance,  which,  itself,  was 
flanked  by  towers  on  the  exterior  and  closed  with  massive 
doors;  the  tortuous  passage,  which  led  from  the  towers  to 
the  interior  of  the  castle,  l)eing  further  secured  by  a  grated 
portcullis  which  could  be  dropped,  at  a  moment's  notice, 
to  arrest  a  sudden  assault.  Besides  the  ordinary  measures 
of  loop-holes  and  machicoulis  in  the  walls  and  towers  for 


220  SUMMARY   OF   THE    PROGRESS    OF   FORTIFICATION. 

aniioyii)*^  the  assailant,  a  lii<;li  interior  tower,  termed  a 
kee]),  or  donjon  was  often  added,  wliicli,  conmuinding  the 
exterior  defences,  served  also  as  a  watch-tower  over  the 
adjacent  country. 

672... The  keep,  being  the  last  defensible  point,  was  in 
some  cases  provided  with  a  secret  subterranean  passage, 
having  its  outlet  in  a  distant  concealed  spot,  through 
which  succor  could  be  introduced  into  the  beleaguered 
castle  and,  in  the  last  extremity,  the  garrison  lind  safety 
in  a  stealthy  flight. 

673... The  fortifications  of  towns  partook  of  the  same 
characteristics  as  those  of  castles.  From  the  custom  of 
assigning  to  the  different  burgher  crafts,  each  of  which 
had  an  independent  military  organization,  the  exclusive 
guardianship  of  portions  of  the  enceinte,  as  Avell  as  their 
erection  and  repairs,  great  diversity,  and,  frequently,  a 
whimsicality,  in  the  defensive  arrangements,  was  the  natu- 
I'ul  result;  the  evidence  of  which  still  exists  in  the  remains 
of  the  walls  of  some  of  the  old  continental  cities.  The 
art,  for  the  most  part,  w^as  practised  l)y  ambulatory  en- 
gineers, who,  like  the  secret  orders  by  whom  tlie  bridges 
and  churches  of  the  same  period  were  Imilt,  offered  their 
services  wherever  they  were  wanted.  Many  new  ideas 
were  also  introduced  from  the  East  by  the  Crusaders,  as 
exhibited  in  the  fortifications  of  castles  and  cities  belong- 
ing to  the  templars  and  other  religious  military  orders. 

674... With  the  invention  of  gunpowder  and  its  applica- 
tion to  military  purposes,  a  gradual  revolution  took  jilace 
in  the  general  forms  and  details  of  fortification.  It  was 
soon  seen  that  naked  walls  alone  did  not  afibi-d  space 
enough  for  the  new  military  machines,  nor  sufKcicnt  i)ro- 
tection  against  the  projectiles  thrown  from  them.  This 
led  to  the  introduction  of  earthen  ramparts  and  parapets, 
which  were  placed  against  the  walls  and  suitably  arranged 
to  meet  the  exigencies  arising  from  this  change.  The  art 
began  to  receive  something  like  a  scientific  basis  about 
this  time  in  Italy,  from  which  the  names  and  forms  of 
most  of  the   elements  of  fortification   now  in   use   are  de- 


SUMMARY    OF    THE    PROGRESS    OF    FORTIFICATION.  221 

rived.  The  Italian  engineers,  like  their  predecessors,  went 
from  state  to  state  to  offer  tiieir  services  wherever  tliej- 
were  needed,  and,  in  this  way,  disseminated  the  })rinciples 
of  tlieir  scliool  througliont  Enrope.  It  was  at  this  epoch 
that  the  bastioned  form  of  fortitication  tirst  appeared,  bnt 
the  precise  date  and  the  author  of  the  invention  arc  botli 
unknown.  With  its  introduction,  tlie  importance  of  sep- 
arating the  parts  of  a  line  of  fortification  into  advanced 
and  retired  parts,  the  latter  flanking  and  defending  the 
former,  seems  to  have  been  recognized  as  an  essential 
principle  of  the  art.  With  these  changes  in  the  form  <^i 
the  enceinte  the  art  was  gradually  improved,  by  the  addi- 
tion of  outworks  to  increase  the  amount  of  cross  and  flank 
fire;  the  introduction  of  bomb-proof  shelters  for  the  troops 
and  other  })nrposes;  the  substitution  of  earthen  for  stone 
pai-apets;  and  the  attempt  to  conceal  the  scarp  walls  from 
the  enemy's  batteries,  by  decreasing  the  command  and 
deepening  the  ditches  of  the  enceinte. 

675... By  these  gradual  changes,  stone  walls,  which  in  the 
old  fortifications  were  the  essential  defensive  features,  came 
at  length  to  be  regarded  in  their  true  character,  simply  as 
passive  obstacles  to  an  open  assault  by  escalade.  The  prop- 
erty of  earthen  parapets  of  resisting,  without  material  loss 
of  strength,  the  long  continued  fire  of  the  assailant's  heav- 
iest guns,  showed  that  the  same  defensive  means  w^ere 
applicable  both  to  works  of  a  permanent  and  of  a  tempo- 
rary character,  and  were  e({ually  available  for  the  purposes 
of  the  assailant  and  the  assailed.  The  measures  for  the 
attack  and  for  the  defence  of  positions  were  thus  reduced 
to  the  same  general  principles,  diftering  only  in  the  forms 
and  dimensions  of  the  elementary  parts,  as  circumstances 
seemed  to  denumd. 

676... Italian  School.  As  above  stated,  the  first  employ- 
ment of  bastions,  as  they  now  exist,  was  made  by  the  Italian 
engineers;  and,  as  far  as  has  been  ascertained,  toward  the 
close  of  the  fifteenth,  or  the  commencement  of  the  six- 
teenth century.  To  whom  the  credit  of  their  invention  is 
due,  is   not  known.     In   the  earlier  fronts  of  the  Italian 


222  SUMMARY    OF   THE    mOGRESS    OF   FORTIFICATIOX. 

school  tlio  l)asti()ns  are  very  small,  and  they  are  connected 
hv  curtains  varying  from  2o0  to  500  yards  in  length.  The 
bastion  Hanks,  ^vhich  >yere  nsually  perpendicular  to  the 
curtains,  were  divided  into  two  portions:  that  next  to  the 
curtain,  which  was  one-third  of  the  entire  Hank,  was  thrown 
back,  and  covered  by  the  portion  in  advance;  the  advanced 
portion,  thus  formed,  received  the  name  of  the  orilloii.  The 
lower  part  of  the  retired  portion  was  casemated  for  cannon; 
and  behind  this,  and  separated  from  it  by  a  dry  ditch,  rose 
a  second  Hank,  having  the  same  command  as  the  otlier 
parts  of  the  enceinte  parapet.  In  some  cases,  a  small  and 
very  obtuse  bastion  was  erected  at  the  middle  of  long  cur- 
tains. The  ditches  of  the  enceinte  were  usually  about  100 
feet  wide,  and  24  feet  deep,  the  counterscarps  being  par- 
allel to  the  bastion  faces.  A  scarp  gallery,  for  the  purpose 
of  mining,  ran  throughout  the  enceinte  scarp,  and  commu- 
nicated with  galleries  leading  to  other  points.  The  par- 
apets, at  first  of  masonry,  were  afterward  of  earth,  and 
made  from  18  to  24  feet  thick.  The  earth  of  the  ram}nirt 
was  sustained  on  the  interior  by  a  wall.  Ramps  estab- 
lished a  communication  between  the  interior  and  the  ram- 
part. 

G7T...Tlie  defects  of  these  early  frc^nts  were  soon  felt,  and 
a  more  coni[>Iicated  but  inij)roved  tra(;c  adopted,  in  which 
the  bastions  were  enlarged,  and  the  curtains  diminished. 
The  retired  Hanks  were  still  retained,  l)ut  the  orillon,  in- 
stead of  l)eing  angular,  was  rounded.  To  these  inipiH)ve- 
ments  cavaliers  were  sometimes  added  to  the  bastions, 
which,  in  those  cases,  were  made  without  retired  flanks, 
or  they  were  placed  on  the  curtains,  when,  from  the  con- 
figuration of  the  site,  some  portion  of  tlie  ground  within 
cannon  range  could  not  be  swe})t  from  the  enceinte  par- 
apet. The  covered-way  was  introduced,  and  became  an 
integral  part  of  the  front;  and  a  small  demilune,  or  rave- 
lin was  placed  in  advance  of  the  enceinte  ditch,  forming  a 
tete  de  pout  to  cover  the  communication,  at  the  middle  of 
the  curtain  across  the  main  ditch,  between  the  enceinte 
and  the   exterior.      The    covered-way,   which  at   first    was 


SUMMARY    OF    THE    PROGRESS    OF    FORTIFICATION.  223 

of  uniform  width,  and  Lordcred  the  main  and  deniihme 
ditches,  Avas  subsequently  provided  witli  salient  and  re- 
entering places  of  arms.  These  various  essential  parts  of 
a  fortified  front  were  gradual!)-  ameliorated  l)y  the  Italian 
engineers,  hut  not  before  the  Italian  scliool  had  left  its 
impress  upon  the  fortification  of  all  the  other  states  of 
Europe,  as  the  Italian  engineers,  from  tlieir  superior  ac- 
quirements, were  in  demand  throughout  these  s*^ates. 

678... Spanish  School.  This  school,  as  seen  in  the  ex- 
isting fortifications  of  S[>ain,  shows  tlie  influence  of  the 
Italian  school,  though  modified  by  national  characteristics. 
These  are  observed  in  the  greater  dimensions  given  to  their 
profiles,  an  augmentation  of  the  means  of  annoying  the 
besiegers  by  artillery  and  musketry,  the  construction  of 
complex  interior  retrenchments,  and,  frequently,  the  omis- 
sion of  a  covered-way ;  tlie  entire  organization  of  the  works 
pointing  toward  an  obstinate  passive  defence,  rather  than 
to  one  in  wliich  sorties  may  phiy  an  essential  part — a  mode 
of  defence  in  which  the  Spaniards,  at  all  periods  of  their 
history,  have  exhil)ited  consummate  skill  and  persever- 
ance. 

From  the  broken  character  of  numy  of  the  sites  of  their 
fortifications,  the  Spanish  engineers  have  resorted  to  de- 
tached works  to  occupy  commanding  positions  in  advance 
of  the  main  work.  These  detached  works  are  also  organ- 
ized for  a  purely  passive  defence;  being  left  to  their  own 
resources  rather  than  to  any  support  from  the  main  work. 

G79... Dutch  School.  This  school  took  its  rise  in  the 
political  necessities  of  the  times,  in  which  the  national 
sjiirit  was  aroused  to  throw  off  an  onerous  foreign  yoke. 
The  aquatic  character  of  Holland,  and  the  want  of  time 
and  pecuniary  means,  suggested  those  expedients  of  de- 
fence which  are  never  wanting  under  like  circumstances. 
The  deficiency  of  earth  led  to  the  formation  of  low  para- 
pets for  the  main  enceinte,  and  wide  ditches  filled  with 
water.  The  nniin  enceinte  was  usually  jneceded  1)y  a 
second  one  with  a  very  low  parapet,  to  swee}>  the  surface 
of  the  wet  ditch  ;  and  this  second  enceinte  was  separated 


224  SUMMARY    OF   THE    PROGRESS    OF   FORTIFICATION. 

from  the  first  by  a  dry  ditch,  which  favored  sorties,  and 
wliich  was  provided  with  all  the  means,  as  palisades,  tam- 
bours and  lilock-houses,  for  offensive  returns  and  surprises. 
The  second  enceinte  was  covered  by  a  glacis  in  advance  of 
the  main  ditch.  The  covcred-way  left  between  the  glacis 
and  the  ditches  was,  to  a  great  extent,  frequently  dc[)rived 
of  its  essential  offensive  feature,  by  the  introduction  of  an 
exterior  wet  ditch,  placed  at  the  foot  of  tlie  glacis  and 
enclosing  it;  over  which  communication  with  the  exterior 
was  kept  open  by  temporary  bridges.  The  works  were 
usually  greatly  multiplied  and  their  combination  compli- 
cated. The  whole  of  the  defensive  measures  of  this  school 
seem  to  have  had  for  their  object  a  strictly  passive  resist- 
ance. AVitli  this  view,  long  lines  of  intrenchments,  sup- 
ported, from  distance  to  distance,  by  forts,  connected  their 
frontier  towns  and  villages,  affording  a  sufhcient  obstacle 
to  marauding  expeditions,  l)y  requiring  the  efforts  of  a 
strong  force  to  break  through  them.  At  a  later  period, 
taught  by  the  experience  of  their  earlier  efforts  against  the 
most  military  state  of  that  epoch,  covers  that  would  afford 
security  against  incendiary  modes  of  attack  were  provided  ; 
and  revetements  of  masonry  substituted  for  the  earthen 
slopes  of  the  ramparts,  particularly  where  the  ditches  were 
dry.  These  successive  changes,  partly  induced  by  the  Ita- 
lian and  Spanish  schools,  with  whose  methods  the  Dutch 
engineers  became  acquainted  through  their  connection 
with  Spain,  were  the  natural  precursors  of  the  methods  of 
Coehorn,  the  most  distinguished  engineer  of  the  Dutch 
school,  whose  works  are  characterized  by  many  of  its  es- 
sential features. 

680... German  School.  The  Germans  reckon  a  number 
of  original  writers  on  fortification,  among  the  most  noted 
of  whom  are  the  celebrated  painter  Albert  Durer,  Daniel 
Speckles,  and  Rimpler.  In  the  propositions  of  these  wri- 
ters are  to  be  found  the  influence  which  the  Italian  school 
naturally  exercised  throughout  civilized  Europe,  and  the 
germs  of  many  of  the  views  held  by  the  German  school 
of  the    present  day,   which    last  seem,  however,   to    have 


SUMMARY    OF   THE    TROGRESS    OF    FORTIFICATION.         225 

been   taken  more  immediately  from    the   propositions   of 
Montalcmbert  and  Carnot. 

681... Swedish  School.  Tlie  part  played  by  Sweden  np- 
on  the  theatre  of  Europe,  under  her  two  cclel)rated  nion- 
archs,  Gustavns  Adolphus  and  Charles  XII,  served  to  de- 
velop in  this  nation  every  branch  of  the  military  art.  A 
number  of  distinguished  generals  and  engineers  arose  un- 
der these  monarchs,  who  combined,  with  the  practice  of 
their  profession,  a  study  of  its  theory.  Among  the  engi- 
neers of  this  school  Virgin  holds  the  first  place.  The 
climate  and  the  nautical  habits  of  a  large  portion  of  the 
inhabitants  seem  to  have  led  to  the  construction  of  land 
defences  analogous  to  those  of  ships:  as  shown  in  the  use 
of  casemated  batteries  in  several  tiers,  both  for  sea-coast 
and  inland  fortifications.  In  this  school  the  bastioned 
system  seems  to  have  been  generally  adopted  for  the  en- 
ceinte, great  attention  being  paid  to  covering  the  faces  of 
the  wTjrks  from  enlilading  fire,  to  providing  casemates 
having  reverse  views  on  the  besieger's  works,  and  par- 
ticularly in  so  arranging  the  interior  defences  that  each 
part  should  not  only  contribute  to  the  support  of  the 
others  but  be  capable  of  an  independent  resistance.  These 
dispositions  necessarily  led  to  a  great  complication  and 
multiplicity  of  works,  as  shown  in  the  writings  of  Vii'gin. 

682... French  School.  What  may  be  termed  the  char- 
acteristics of  this  school  are  to  be  seen  rather  in  the 
method  of  Cormontaingne,  and  the  teachings  of  the  two 
celebrated  schools,  Mczieres  and  Metz,  for  the  education 
of  engineers,  than  in  the  practice  of  Vauban,  although 
his  authority  has  exercised  a  preponderating  influence 
througiiout  Europe;  and  is  still  appealed  to,  in  all  great 
problems  of  the  art,  by  each  side  in  polemical  dis[)utes. 
The  French  have  evinced  in  this,  as  in  all  the  other  arts, 
that  spirit  of  s^-stematic  combination  which  forms  one  of 
their  most  striking  national  traits.  Without  excluding 
an  active  defence,  the  most  noted  authors  of  this  school 
have  based  their  methods  more  upon  a  combination  of 
elements  by  whii-h  the  besieger's  progress  can  be  checked, 
15 


226  PROGRESS    OF    THE    ATTACK 

Step  by  stop,  by  tbc  lire  of  tbc  works  tban  by  sorties. 
Until  witbin  the  last  thirty  or  forty  years,  tlie  French 
school  was,  perhaps,  open  to  the  reproach  of  a  too  exclu- 
sive method,  and  a  subjection  to  mere  authority.  Tliis 
accusation,  however,  was  true  rather  of  the  polemical  writ- 
ings of  the  day,  growing  out  of  the  propositions  of  Mon- 
talenibcrt,  than  of  the  practice  of  the  French  engineers; 
and  it  was,  in  a  measure,  strengthened  by  a  misconception 
on  the  part  of  foreign  engineers,  of  the  real  pur[)Oses  of 
the  instruction  given  in  their  schools  of  professional  train- 
ing. Still,  recognizing  in  Vauban  and  (Jormoutaingne  the 
chief  founders  and  authorities  of  their  school,  the  Frencli 
engineers  of  the  present  day  discard  no  defensive  element 
that  has  stood  the  test  of  experience,  or  is  consonant  with 
sound  professional  views.  Basing  their  art  upon  incon- 
trovertible principles,  its  practice  is  made  by  them  to  con- 
form to  the  exigencies  of  eacli  case  as  presented  by  its 
own  data. 


.jJroijrcfif)  of  the  gitfacli  liiiue  the  Jnucutinu  of[ 


xfirearmfi. 


683... The  introduction  of  cannon,  althougli  it  led  to 
important  changes  in  the  measures  both  of  the  attack 
and  defence,  still  did  not,  for  a  considerable  period,  bring 
about  any  very  decisive  results  in  tlie  lengtli  of  sieges. 
The  means  which  it  afforded  the  defence  of  reaching  the 
besiegers  at  a  distance,  and  destroying  all  the  methods 
of  ap[)roaching  and  annoying  the  place  whicli  liad  been 
liitbcrto  used,  led  to  the  substitution  of  the  ordinary 
trenches  of  the  present  day  for  the  wooden  galleries  and 
other  similar  ex[)edients  for  approaching  under  cover; 
and  to  the  ei'ection  of  l)atteries  at  distant  points  to  ojien 


SINCE    THE    INVENTION    OF    FIllEAllMS. 


•■>v7 


breaches  in  the  walls.  Lines  of  circunivallation  and  coun- 
tci'vallation,  which  formed  so  prominent  a  feature  pre- 
viously to  this  epoch,  was  the  only  one  which  still  kej)t 
its  place,  as  it  has  done  to  a  greater  or  less  extent  to  the 
present  day.  For  the  purpose  of  effecting  an  entrance 
into  the  place,  breaching  l)atteries  Avere  erected  opposite 
the  points  deemed  most  favorable.  They  were  placed 
either  on  natural  elevations  of  the  ground  or  u})on  ai'ti- 
ficial  mounds,  with  the  object  of  attaining  the  wall  to  be 
opened  near  its  foot  and  thus  form  a  breach  of  eas}'  ascent. 
These  batteries  were  enclosed  in  works  of  sufficient  size 
and  strength  to  hold  garrisons  to  secure  them  from  sorties. 
The  approaches  were  made  as  at  present  l)y  zig-zags,  along 
the  capitals  of  the  salients,  to  the  counterscarp,  where  a 
covered  descent  was  made  into  tlie  ditch,  opposite  the 
l)reach,  preparatory  to  its  assault.  AVhen  the  wall  was 
not  exposed  to  a  distant  fire,  the  besiegers  were  obliged 
to  carry  the  covered-way  by  assault  and  establish  their 
breaching  batteries  on  the  crest  of  the  glacis.  In  carry- 
ing forward  these  Avorks,  the  besiegers  were  subjected  to 
great  losses  and  dehiys,  owing  to  the  magnitude  and  mul- 
tiplicity of  the  works  they  were  obliged  to  comitlete  ;  to 
ihc  imperfect  character  of  their  artillery  and  the  faulty 
]M)sitioii  <'f  tlieir  batteries,  by  which  they  were  unal)Ie  to 
keep  under  the  tire  of  the  place  ;  the  want  of  connection 
between  the  sejiarate  approaches ;  and  the  exposure  of  the 
workmen  in  the  trenches  to  sorties,  the  troops  for  tlieir 
support  in  the  enclosed  works  in  the  rear  being  too  dis- 
tant to  give  timely  succor;  besides  this,  as  these  enclosed 
works  naturally  became  the  chief  objects  for  the  fire  of  the 
besieged,  the  agglomeration  of  troo})S  in  them  added  ma- 
terially to  the  losses  of  the  besiegers.  Owing  to  these 
imperfections  in  the  measures  of  attack,  the  besieged  were 
able  to  make  a  vigorous  and  prolonged  defence;  sieges 
l)C<'ame  the  most  imjiortant  military  operations  of  this 
period,  in  which  captains  of  the  greatest  celebrity  sought 
for  opportunities  of  distinction. 

()(S4...I>ut  little  deviation  was  nnuU- in  the  methods  just 


22S  PROGRESS  OF  THE  ATTACK 

described,  until  ^':^nball  appeared  upon  the  scene.  Pre- 
viously  to  liini,  Montluc,  a  distinoruishcd  French  general 
and  engineer  of  his  day,  had  intro(hiced  short  branches  of 
trenches,  which  were  run  out  from  the  angles  of  the  zig- 
zuics,  to  post  a  few  troops  for  the  immediate  protection  of 
the  workmen,  but  these  were  found  to  l)e  very  insufficient 
in  repelling  sorties  of  any  strength.  The  event  which 
seems  to  have  had  the  greatest  influence  on  the  subse- 
quent progress  of  both  the  attack  and  defence  was  the 
memorable  siege  of  Candia,  in  which  volunteers  from  all 
parts  of  Europe  were  engaged,  who,  after  its  close,  dis- 
seminated tbroughout  their  respective  countries  the  results 
of  the  experience  they  had  there  acquired.  Whether  the 
idea  of  the  parallels,  now  in  use  in  the  attack,  originated 
there,  or  witb  Vauban,  this  eminent  man  was  the  first  to 
establisb  them  in  a  systematic  manner,  and  to  demonstrate 
by  experience  their  controlling  importance  in  repressing 
sorties.  The  introduction  of  this  important  element  in 
the  attack ;  the  concentration  of  the  fire  of  batteries,  by 
giving  them  enfilading  positions;  the  invention  of  the 
ricochet,  as  the  most  powerful  destructive  means  against 
the  defences ;  the  avoidance  of  oi)en  assaults,  which,  even 
when  successful,  are  made  at  a  great  sacrifice  of  life,  pre- 
ferring to  them  the  less  brilliant  but  slower  method  of  skill 
and  industry,  by  which  the  Itlood  of  the  soldier  is  spared, 
and  the  end  more  surely  attained,  sucli  are  the  importaiit 
services  which  the  attack  owes  to  Vauban  ;  which  has 
given  it  its  present  marked  superiority  over  the  means 
of  defence;  and  to  which  the  science  and  experience  of 
engineers  since  bis  day  have  added  nothing  of  marked 
importance. 

685... Conclusion.  Whilst  the  attack  has  thus  been 
brought  to  such  a  state  of  perfection,  and  its  destructive 
means  are  still  on  the  increase,  from  the  rapid  improve- 
me!it  daily  making  in  the  range  and  certainty  of  aim  of 
cannon,  as  well  as  in  the  ease  with  which  the  most  gigantic 
armaments  can  be  now  transported  to  distant  points,  both 
on  sea  and  land,  the  means  of  defence,  so  far  as  relates  to 


SINCE    THE    INVENTION    OF    FIllEARMS.  229 

fortification  alone,  are  but  little,  if  at  all,  in  advance  of 
what  they  were  in  the  time  of  Yauban.  Upon  the  chief 
defects  and  wants  of  the  art,  there  exists  but  slight  diver- 
gence of  ojtinion  among  engineers  generally;  not  so  with 
respect  to  the  renied\' ;  opposite  oi)inions  being  frequently 
drawn  from  the  same  class  of  facts,  and  the  same  authority 
frequently  cited  to  sustain  opposite  views.  Whilst  each 
new  disputant  denounces  systematizing  and  tlie  systems  of 
others,  his  remedj'  for  the  abuse  complained  of  is  usually 
a  system  of  his  own,  which  not  unfrequently  offers  l)ut 
the  disjecta  membra  of  those  of  others.  The  sum  of  the 
wliole  matter  is,  that  fortification  is  an  art  the  component 
elements  and  principles  of  which  are  few  and  simple.  Its 
efficiency  consists  neither  in  short  lines  of  defence  nor  l')ng 
lines  of  defence;  nor  in  large  or  snnUl  bastions;  uor  in  tlie 
adoption  of  this  or  that  s\-steni ;  but  in  the  judicious  adap- 
tation of  these  princi[)les  and  elements  to  the  locality  to  be 
defended,  and  the  purposes  of  the  defence.  In  this  resides 
the  excellence  of  the  engineer's  art.  lie  who  should  com- 
bine his  elements  in  the  arrangement  of  a  small  work, 
with  a  weak  garrison,  as  in  one  intended  for  the  occupa- 
tion of  an  extensive  position  by  a  large  force,  or  should 
blindly  adopt  the  same  methods  for  an  irregular  site 
that  he  would  for  a  horizontal  one,  whatever  his  acquisi- 
tions or  pretensions  may  be,  has  but  a  small  claim  on  the 
title  of  military  engineer. 

686... From  the  preceding  brief  summary,  it  will  be  seen 
tliat  the  art  of  fortification,  in  its  progress,  has  kept  jiace 
with  the  measures  of  the  attack  ;  its  successive  changes 
having  been  brought  about  by  changes  either  in  the  arms 
used  by  the  assailant,  or  by  the  introduction  of  some  new 
mode  of  assault.  The  same  causes  must  continue  to  pro- 
duce the  same  effects.  At  no  past  i)eriod  has  mechanical 
invention,  in  its  bearing  on  the  militar}-  art,  been  more 
active  than  at  the  present  (hiy.  The  improvement  that 
has  already  been  made  in  the  range  and  accuracy  of  aim 
of  both  small  arms  and  cannon,  the  partial  ado})tion  of 
wrought-iron  and  steel  for  floating  batteries  and  sea-coast 


230  PROGRESS    OF   THE    ATTACK. 

defences,  point  to  tlie  conimenceniciit  of  aiiotlior  irnpoi-tant 
epoch  \u  the  engineer's  art.  Tl)e  <^reat  improvomont  in 
cannon  Avill  give  to  the  assailant  a  still  wider  range  in 
the  selection  of  positions  for  his  batteries,  and  will  thus 
increase  the  difficnlties  of  tlic  engineer  in  adapting  his 
works  to  tlie  site,  and  in  giving  adequate  shelter  to  the 
garrison  and  armament.  Whilst  the  defence  Avill  be  to 
this  extent  weakened,  the  approaches  of  tlie  ])esiegcr  will 
be  rendered  more  perilous  and  more  difficult,  from  the 
greater  range  and  accuracy  of  small  arms.  The  great 
destruction  of  life,  in  open  assaults,  by  columns  exposed 
within  so  long  a  range,  must  give  an  additional  value  to 
intrenched  fields  of  battle:  and  we  mav  aijain  see  field- 
works  play  the  part  they  did  in  the  defence  of  Sebastopol ; 
and  positions  so  chosen  and  fortified  that  not  only  will 
the  assailant  be  forced  to  intrench  himself  to  assail  them, 
but  will  find  the  varying  phases  of  his  attack  met  by  cor- 
responding changes  in  the  defensive  dispositions. 

087. ..The  engineers  of  our  own  country,  without  ser- 
vilely copying  any  of  the  systems  in  vogue  in  Europe, 
have,  in  most  of  their  enclosed  works  of  any  size,  adopted 
the  bastioned  system.  As  the  works  erected  hy  them  are 
chieflv  for  sea-coast  defence,  their  water  fronts  usually 
consist  of  one  or  more  tiers  of  casemates  surmounted  by  a 
barbette  battery ;  whilst  the  land  fronts  present  a  rampart 
arranged  for  open  defences.  In  small  works,  where  the 
properties  of  the  bastioned  system  could  not  be  developed, 
owing  to  the  limited  size  of  the  fronts,  flanking  disposi- 
tions have  been  made,  either  by  casemated  capon niiires 
or  l)y  counterscarp  galleries;  and,  in  cases  where  a  large 
amount  of  fire  was  requisite  to  sweep  a  given  approach  by 
sea,  they  have  resorted  to  the  castellated  form  of  casennited 
batteries;  combining  several  tiers  of  casemates  with  a  bar- 
bette battery  on  top, 

AVhilst  thus  adhering  to  well  settled  principles  and  the 
practice  of  the  l)est  European  authorities,  our  engineers 
have  contributed  their  share  to  the  improvement  of  the 
details   (»f  the   ai't.     The  works   erected   bv   them,    within 


INFLUENCE    OF    IRIIEGULARITIES    OF    SITE.  231 

the  last  thirty  or  forty  years,  are  remarkable  for  the  excel- 
lence of  the  materials  employed  l)y  them,  the  superior  skill 
shown  in  the  workiminship,  and  the  care  with  which  every 
detail  is  worked  out  to  subserve  the  object  in  view.  In 
these  respects  and  in  the  general  adaptation  of  the  plan  to 
the  site,  it  is  not  claiminii;  too  much  to  say  that  the  works 
erected  by  them  are  not  surpassed  and,  in  some  points,  not 
equalled  b}'  any  similar  works  in  Europe. 


^ 


|n)1uencc  of  Jrrrgularifics  of  .^itc  on  the  (Jforni!) 

niul  (Ijambinationfi  of  the  Oilniirntfi  of 

|jenn;inent  Mloiiifi. 


688... In  treating  the  subject  of  permanent  fortification, 
the  same  order  is  usually  followed  as  in  the  discussion  of 
temporary-  fortification,  viz:  1st.  An  exposition  of  the 
general  principles  with  their  applications  to  a  horizontal 
site.  2d.  The  various  modifications  of  detail  occasioned 
by  irregularities  of  site  as  presented  in  nature.  3d.  The 
various  accessory  means  of  strengthening  weak  points, 
called  for  b}'  peculiar  circumstances  of  locality,  which 
either  preclude  the  aitplication  of  the  ordinary  means  or 
require  others  in  addition  to  them. 

689. ..Whether  the  site  is  perfectly  level  within  the  range 
of  the  fire  of  the  work  or  is  irregular,  the  same  general 
conditions  are  to  be  satisfied  in  each  case,  in  order  that  the 
work  shall  have  all  the  efliciency  of  which  it  is  capable. 
These  are:  Ist.  That  every  point  exterior  to  the  defences 
over  which  the  enemy  must  approach  them,  or  from  wliich 
he  can  annoy  them  by  his  fire,  should  Ite  brought  under 
the  fire  of  the  defences.  2d.  That  no  point  of  the  de- 
fences shall  be  left  ungnarded  by  their  own  fire,  or  present 


232       INFLUENCE  OF  IRREGULARITIES  OF  SITE. 

any  position  wliere  the  enemy,  obtaining  temporary  slielter 
from  lire,  may  gain  time  to  renew  an  onset.  3cl.  That 
the  troops  and  materiel  within  tlie  defences  sliall  he  shel- 
tered from  the  enemy's  tire  in  any  position  lie  may  take 
exterior  to  them. 

690.. ..The  problem  presented  for  solution  to  the  en- 
gineer in  irregular  sites  is,  frequently,  one  of  no  ordinary 
complexity;  demanding  a  minute  and  lal)orious  study  of 
the  natural  features  of  the  position  in  their  relations  to  the 
defence;  connected  with  a  tentative  process,  of  which  the 
object  is  so  to  modify  the  plan,  relief  and  details  ordinarily 
adopted,  as  to  ada})t  them  in  the  best  manner  to  the  given 
position.  No  rules,  but  of  a  very  general  character,  can 
be  laid  down  for  the  guidance  of  the  engineer  in  such 
cases.  Of  this  class  the  following  are  the  most  obvious 
and  essential,  and,  when  practicable,  should  be  adhered  to. 

691... 1st.  It  has  already  been  observed  that,  from  the 
means  used  in  the  attack  of  permanent  works,  the  more 
plunging  the  fire  of  the  work  the  more  efficacious  will  it 
prove  in  retarding  the  enemy's  i)rogress.  The  elUeiency 
of  this  tire  will  depend  upon  two  causes,  the  command 
of  the  work  over  the  jtoiiit  to  he  attained,  and  the  direc- 
tion of  the  ground  with  respect  to  the  lines  by  wiru-h  it 
is  swept. 

692... As  to  the  command  of  the  work  over  the  exterior 
ground,  it  has  already  been  shown  that  motives  of  economy 
restrict  it,  in  most  cases,  within  very  narrow  limits,  where 
to  obtain  it  artificial  embankments  have  to  be  emi)loyed. 
To  augment,  therefore,  in  the  greatest  degree  this  element 
of  the  defence,  advantage  should  be  taken  of  the  natural 
features  of  the  locality,  l)y  placing  the  princii)al  lines,  from 
which  the  exterior  ground  can  be  seen,  on  the  most  com- 
niiiiidiiig  or  highest  ])()ints  of  the  site.  If,  with  this  posi- 
tion given  to  the  principal  lines,  the  ground  swept  falls,  or 
slopes  toward  them,  the  most  favorable  combination  for  an 
efficacious  i)lunging  fire  will  be  obtained;  for,  with  this 
direction  of  the  ground,  the  enemy  will  meet  with  far 
greater    difficulty,    to   put   himself   under   shelter    by    his 


INFLUENCE    OF    IRREGULARITIES    OF    SITE.  233 

works,  than  where  the  ground  fulls,  or  slo})es  from  the 
line  by  which  it  is  swept;  us  the  surfuce,  in  the  lutter 
cuse,  descending  in  the  reur  of  the  cover  thrown  up  by 
the  enemy,  will  be  screened  to  u  greuter  extent  thun  in 
the  former,  where  it  rises  in  the  reur  of  the  cover. 

693. ..The  general  rule,  therefore,  which  the  engineer  is 
to  tuke  us  u  guide,  in  order  to  sutisfy  the  condition  of 
bringing  the  exterior  ground  under  un  efficucious  lire  from 
the  work,  is  to  place  the  principal  lines  of  his  work  on  the  most 
commanding  pioints  of  the  site,  and  in  such  directions  as  to  bring 
the  exterior  ground  to  be  swept  in  a  position  sloping  tovxird  these 
lines;  und  this  will  generally  be  best  eft'ected  by  plucing 
the  salient  points  of  the  work  on  the  most  commanding 
and  salient  points  of  the  site  ;  as,  in  this  position  of  the 
salients,  the  faces,  which  are  usually  the  principal  lines 
bearing  on  the  exterior  ground,  will  occupy  the  sulient  und 
commanding  portions  of  the  site,  whilst  the  re-enterings, 
being  thrown  on  the  re-entering  und  lower  portions  of  the 
site,  will  be  in  the  best  position  for  sweeping  the  ground 
immediately  in  advance  of  the  faces;  and,  at  the  same 
time,  the}'  will  be  masked  by  the  faces  from  the  enemy's 
view,  and  thus  preserved  from  serious  injury  up  to  the 
moment  when  tlieir  action  may  be  rendered  most  eit'ec- 
tive;  that  is  when  the  enemy,  despite  the  fire  from  the 
faces,  has  succeeded  in  planting  himself  upon  points  on 
which  this  fire  cunnot  longer  be  brought  to  beur. 

694. ..2d.  The  condition  of  leaving  no  point  of  the 
defences  unguarded  by  their  fire,  will  depend,  in  a  great 
degree,  for  its  fulfilment  on  the  same  rule  as  the  preced- 
ing. But  where  both  conditions  cannot  be  satisfied,  the 
distant  defence  should  be  sacrificed  to  the  near,  as  upon 
the  latter  the  more  or  less  of  obstinacy  of  resistance 
depends,  since  the  fire  of  the  work  and  the  action  of 
the  garrison  are  the  more  efl^ective  as  the  point  to  be 
guanled  is  the  nearer  to  the  defences. 

695. ..8d.  The  condition  that  the  troops  and  materiel 
witliin  the  defences  shall  be  sheltered  from  tlie  enemy's 
fire,   from   all    commanding   points   without,   will    depend 


234  INFLUENCE    OF    IRREGULARITIES    OF    SITE. 

upon  the  relative  positions  of  the  principal  lines  and  the 
exterior  commanding  points;  and  as  far,  therefore,  as  it 
can  be  done,  withont  sacriiicing  eitlier  of  the  preceding 
and  more  important  conditions,  the  plan  of  the  work 
should  he  so  arranged  that  the  })rincipal  lines  shall  pre- 
sent themselves  in  the  most  fav()ral)Ie  direction  to  the 
exterior  ground  to  avoid  }»hinging,  enii hiding  or  reverse 
views  upon  their  terrepleins  from  any  point  of  it. 

696... To  effect  these  objects,  when  the  work  is  in  the 
vicinity  of  commanding  heights  within  cannon  range,  and 
the  crests  of  these  heights,  as  seen  from  the  work,  present 
a  nearly  horizontal  outline,  the  principal  lines  of  the  work, 
fronting  the  lieights,  should  receive  a  direction  as  nearly 
parallel  as  practicable  to  that  of  the  comnumding  crests; 
when  the  outline  of  the  crests  presents  a  nearly  continuous 
line,  but  one  which  declines  or  slopes  toward  the  site  of 
the  work,  the  principal  lines  toward  the  height  should 
receive  a  direction  converging  toward  the  })oint  where  the 
line  of  the  crests,  as  seen,  if  prolonged  Avould  join  the  site. 

The  reasons  for  the  positions  assigned  to  the  jirini-ipal 
lines,  in  these  cases  respectively,  may  not,  at  a  first  glance, 
be  obvious;  but,  by  examining  the  relative  positions  of  the 
crests  of  the  heights  and  of  the  i)rincipal  lines,  as  here  laid 
down,  it  will,  without  difficulty,  be  seen  that  they  can  be 
brought  in  the  same  })lane,  and  the  latter  be  so  placed  as 
to  give  a  nearly  uniform  command  to  the  para[)ets  of  the 
principal  lines  over  the  site  ;  and  tliat  by  keeping  the  terre- 
pleins of  these  lines  in  })lanes  parallel  to  the  one  in  which 
the  crests  of  the  heights  and  those  of  the  i)arapets  are  held 
and  at  suitable  levels  below  it,  the  parapets  will  be  made 
to  cover  the  terrepleins  from  the  fire  of  the  heights  in  the 
simplest  manner. 

697. ..The  foregoing  general  methods,  for  determining 
the  dii'eelion  of  the  princi})al  lines  fronting  commanding 
heights,  so  ;is  to  cover  from  direct  tire,  in  the  easiest 
manner,  l)y  thcii-  })arapets,  the  s[)ace  to  the  rear  occu[)ied 
by  the  troops  and  materiel^  present,  at  the  same  time,  the 
simplest  cases  of  the  adai)tation  of  the  plan  of  a  work  to 


INFLUENCE    OF    IRREGULARITIES    OF    SITE.  235 

the  features  of  tlie  locality',  to  subserve  the  object  in  view. 
In  most  cases,  all  that  can  be  (h)ne  is  to  avoid  giving  such 
directions  to  any  of  the  principal  lines  as  shall  be  favor- 
able to  entilading  or  reverse  views  of  tlie  enemy;  which 
may  be  etiected  by  so  placing  them  that  their  prolonga- 
tions shall  fall  on  points  where  the  enemy  cannot  establish 
his  works;  or,  on  those  wliich,  if  occupied  by  him,  will 
aftbrd  disadvantageous  positions  for  his  batteries,  cither 
for  enfilading  or  reverse  tires. 

698... Defilement  of  Permanent  Works.  The  greater 
importance  of  so  ada})ting  the  plan  and  command  of  per- 
manent works  to  the  features  of  irregular  sites  as  to  satisfy 
the  conditions  of  sweeping,  thoroughly,  by  their  fire  all 
approaches  exterior  to  the  defences,  and  completely  flank- 
ing the  latter,  seldom  places  it  in  the  power  of  the  engi- 
neer to  fulfil  the  condition  of  withdrawing  the  interior  of 
the  defences  from  either  enfilading  or  reverse  views  by  a 
modification  of  either  the  plan  or  the  command.  To 
shelter  the  terrepleins  which  would  be  exposed  to  these 
fires,  as  well  as  such  as  would  be  attained  by  a  plunging 
fire  in  front,  resort  must  be  had  to  the  usual  expedients  of 
defilement;  that  is,  giving  to  the  terrepleins  such  positions 
with  respect  to  their  parapets  that  the  troops  and  mntcricl 
upon  them  will  be  screened  from  a  plunging  fire  in  fi-ont, 
by  the  parapets;  and,  when  the  terrepleins  are  exposed  to 
either  enfilading  or  reverse  views,  so  placing  earthen  trav- 
erses or  other  masks,  as  to  intercept  these  views,  and 
cover  the  troops,  etc.,  from  the  enemy's  projectiles. 

699. ..The  defilement  of  permanent  works,  like  that  of 
field-works,  proposes  the  same  end,  and  employs  nearly 
the  same  means.  They  differ  mainly  in  their  practical 
details;  the  latter  being  reduced  to  a  simple  practical 
operation  on  the  field,  whilst  the  former,  from  the  usu- 
ally greater  complexity  of  the  arrangements  of  permanent 
defences,  requires  the  aid  of  mathematical  science,  and 
demands  results  of  extreme  accuracy. 

TOC.yor  the  solution  of  all  problems  of  the  dcfilemet)t 
of  permanent  works,  the  engineer  requires  :    1st.  The  limit 


23C       INFLUENCE  OF  IRREGULARITIES  OF  SITE. 

exterior  to  the  defences  beyond  wliicli  the  efteet  of  the 
enemy's  fire  nia}-  be  regarded  as  so  uncertain  as  to  be 
neglected.  2d.  The  presumed  positions  within  this  limit 
that  the  enemy  may  take  up  to  bring  his  artillery  to  bear 
u])on  the  works.  3d.  A)i  accurate  topographical  map  of 
all  the  ground  within  the  above  limits,  as  given  b}-  its 
horizontal  curves  referred  to  a  plane  of  comparison.  4th. 
The  magistrals  and  interior  crests  of  the  works,  as  cither 
definitively  or  approxinuitely  arranged,  referred  to  the 
same  plane. 

701.. ..The  limits  beyond  which  the  enemy's  fire,  from 
the  usual  siege  guns,  may  be  disregarded,  owing  to  the 
uncertainty  of  long  ranges,  are  1,500  yards,  where  the 
w^ork  is  exposed  only  to  a  direct,  or  front  fire;  and  2,000 
yards,  when  open  to  a  reverse  fire.  When  the  terrepleins, 
therefore,  are  covered,  either  by  their  parapets  or  other 
means,  from  batteries  at  these  distances,  they  may  he  con- 
sidered as  ofiering  shelters  sufliciently  secure  for  the  troops, 
etc.,  upon  them. 

702. ..It  may  happen  that  there  are  points  beyond  these 
limits,  but  within  the  extreme  range  of  siege  guns,  which, 
from  their  positions,  it  would  not  be  safe  to  disregard  ;  but 
these  will  form  exceptional  cases,  and,  when  they  occur, 
will  be  treated  in  the  same  manner  as  those  within  the 
limits. 

703. ..The  surface  embraced  within  the  limits  and  the  line 
of  defences,  nia}^  be  divided  into  three  zones:  one  lying  be- 
tween the  limits  and  the  position  of  the  first  parallel  of  the 
attack,  which  is  usually  600  yards  from  the  salients  of  the 
line  of  defences  ;  the  second  between  the  positions  of  the 
first  and  second  parallels,  or  to  a  line  within  about  300 
yards  of  the  salients  just  mentioned  ;  the  third  between 
the  positions  of  the  second  and  third  parallels,  or  up  to 
within  60  yards  of  the  salients.  In  any  position  that  the 
enemy  can  take  up  for  his  batteries,  within  the  first  zone,  it 
is  usually  estimated  that  he  will  not  throw  up  any  parapet 
with  a  greater  command  than  10  feet  over  the  ground  on 
which  it  is  placed.     Granting  this,  the  muzzles  of  his  guns, 


INFLUENCE    OF    IRREGULARITIES    OF    SITE.  237 

heliiiid  the  parapets,  will  not  be  raised  higher  than  6  feet 
above  the  natural  surface;  so  that,  assuming  the  surface  of 
this  first  zone  to  be  raised  6  feet  above  its  true  position, 
this  ma}^  be  regarded  as  the  limit,  vertically,  M'itliin  which 
the  enemy's  lines  of  fire  will  be  restricted ;  and,  therefore, 
if  the  interior  of  the  defences  is  covered  from  the  fire 
within  this  limit,  the  troops,  etc.,  will  be  secure.  That  the 
enemy  will  not,  in  all  likelihood,  elevate  his  guns  above 
this  limit  will  seem  probable,  when  it  is  taken  into  con- 
sideration that  any  advantage  he  might  derive  from  doing 
so  would  not  be  commensurate  to  the  labor  it  would  cost 
him.  For,  suppose  the  enemy  to  have  taken  up  a  position 
for  an  enfilading  battery  at  1,000  yards  from  any  salient, 
to  enfilade  one  of  its  faces  of  the  length  of  100  yards  ;  and 
that  he  should  decide  upon  raising  his  guns  3  feet,  or  one 
yard  above  the  limit  just  laid  down  ;  a  simple  proportion 
Avill  show  that,  by  this  increase  in  the  height  of  his  battery, 
he  will  be  able  to  attain  a  point  at  the  farther  end  of  the 
face  only  3.6  inches  lower  than  he  would  have  done  in  the 
position  of  the  assigned  limit;  an  advantage  which,  consid- 
ering the  uncertaint3'  of  the  fire  at  the  assumed  ranges, 
would  hardly  compensate  the  additional  labor  of  giving  to 
his  works  the  additional  command. 

704... In  the  zone  between  the  first  and  second  parallels, 
the  limit  may  be  reduced  to  4.5  feet,  for  at  this  distance 
from  the  defences  their  fire  is  so  destructive  and  certain 
that  the  enemy  cannot,  without  great  loss  of  life  and  time, 
raise  the  parapet  of  his  batteries  higher  than  8  feet  above 
the  natural  surface. 

705. ..From  the  third  zone,  the  musketry  of  the  enemy 
may  bo  brought  to  l)car  upon  the  defences;  and,  from  this 
position,  during  sorties  from  the  defences,  or  at  any  other 
opportune  moment  when  their  fire  is  not  active,  the  enemv 
might  mount  on  the  parapet  of  his  trenches,  and  from 
there  deliver  his  fire.  This  would  bring  his  line  of  fire 
about  10  feet  above  the  natiiral  surface.  The  limit,  verti- 
cally, of  this  zone  may,  therefore,  be  assumed  at  10  feet 
above  the  natural  surface. 


238  INFLUKNCE    OF    IRREGULARITIES    OF    SITE. 

7OG...TI10  limits  of  the  dangerons  ground  exterior  to  tlie 
line  of  defences  may  be  marked  off  on  the  topograpliieal 
map  of  the  site,  PI.  7,  Fig.  1,  bj'  drawing  lines  concentric 
with  the  line  connecting  the  most  advanced  salients  of  the 
defences,  and  at  the  respective  distances  from  it  of  1,500  or 
2,000  yards  (as  the  lire  may  be  brought  to  bear  on  the  front 
or  rear) ;  600  yards ;  300  3'ards ;  and  GO  yards ;  and  then, 
considering  the  references  of  the  horizontal  curves  of  the 
ground,  within  tlie  zones  thus  marked  off",  to  be  increased 
G  feet  in  the  first;  4.5  feet  in  the  second;  and  10  feet  in 
the  third. 

707... In  the  defilement  of  each  part,  separatel}',  of  the 
line  of  defences,  those  portions  alone  of  these  zones  should 
be  regarded  as  dangerous  which  are  embraced  within  arcs, 
or  other  lines  drawn  at  the  foregoing  distances  from  the 
Salients,  or  the  faces  of  the  part  to  be  defiled.  It  may  also 
happen  that,  within  the  limits  of  dangerous  ground  for  one 
portion  of  the  line  of  defences,  there  ma}^  be  other  portions 
which,  from  their  position,  may  mask  the  portion  to  be 
defiled  from  all  the  dangerous  points  beyond  them  ;  in 
which  case  the  points  thus  shut  off  need  not  be  regarded, 
in  effecting  the  operations  of  defilement.  If,  for  examj)le, 
PI.  7,  Fig.  1,  the  limits  of  dangerous  ground  for  the  demi- 
lune A  being  marked  off*  it  is  found  that  the  demilune  B 
masks  the  demilune  A  from  all  fire  that  might  come  from 
the  ground  beyond  B ;  then  this  portion  of  the  zones  of 
danger  need  not  be  regarded  in  defiling  A.  To  ascer- 
tain this  point,  it  will  be  only  necessary  to  conceive  a  right 
line  to  be  so  moved  as  to  rest  in  each  of  its  positions  u[)on 
a  point  of  the  interior  crest  of  ^  and  on  one  of  J3 ;  and  if 
this  line,  in  all  its  positions,  passes  above  the  surface  of  the 
dangerous  zones  beyond  B,  then  will  B  serve  as  a  nuisk 
fovA. 

70(S...In  covering  masonry'  from  the  eneni^^'s  artillery, 
800  yards  is  usually'  regai'ded  as  the  longest  range  at 
wliich  destructive  effects  can  be  produced ;  and,  also,  that 
within  this  distance  the  angle  of  incidence  of  the  ball  on 
the  suriace  must  be  greater  than  45°,  to  do  serious  injury 
to  it. 


INFLUENCE    OF    IIIREGULAIIITIES    OF    SITE.  239 

709... In  the  defilement  of  works  of  limited  interior 
capacity,  as,  for  example,  the  redoubt  of  the  re-entering 
place  of  arms,  the  double  caponniere,  atid  the  like,  which 
are,  moreover,  not  habitually  occupied  by  trooi)8,  the  ex- 
treme limits  may  be  reduced  to  1,000  or  1,200  yards. 

710... Within  the  limits  of  the  zones  of  danger,  positions 
may  be  found  for  direct  or  front,  for  reverse,  and  for 
enfilading  fire.  If  the  two  faces,  for  example,  of  a  work 
be  prohuiged  to  intersect  the  extreme  limit  of  dangerous 
ground,  the  sector  which  the_y  embrace  may  be  termed  the 
limits  of  direct  ov  front  Jive ;  since,  from  ever}'  position  tbat 
can  be  taken  up  within  this  sector,  a  direct  fire  alone  can 
be  bi-ought  to  bear  upon  the  two  faces.  The  two  sectors 
which  lie  adjacent  to  this  may  be  termed  the  limits  of  lateral, 
or  reverse  fire,  since  they  afford  positions  from  which  a 
reverse  fire  can  be  obtained  against  one  of  the  faces,  and  a 
front  fire  upon  the  other.  It  is  also  only  within  these  last 
limits  that  positions  for  enfilading  the  terrepleins  of  the 
faces  can  be  obtained, 

711. ..The  problems  of  defilement  which  present  them- 
selves for  solution  may  end>race  one  or  more  of  these  cases 
in  any  example ;  depending  upon  the  relative  positions  of 
the  interior  crest  of  the  work  to  be  defiled,  and  of  the  dan- 
gerous ground  embraced  witiiin  the  foregoing  limits.  In 
the  case  of  only  direct  fire,  the  terrepleins  can  be  screened 
by  their  parapets  alone ;  in  that  of  a  reverse  fire  on  cue 
face  alone,  its  terreplein,  in  some  cases,  may  be  screened 
by  a  suitable  position  given  to  the  parapet  of  the  other; 
where  })oth  are  exposed  to  this  fire,  one  or  more  traverses 
must  be  resorted  to  as  a  screen  ;  against  an  enfilading  fire 
on  one  face  alone,  a  portion  of  the  parapet  of  the  other, 
near  the  salient,  may  be  a  sufficient  protection  in  some 
cases ;  but,  for  the  most  part,  traverses,  placed  across  the 
terreplein,  will  be  the  only  remedy. 

712. ..It  docs  not  come  within  the  scope  of  this  summary 
to  examine  the  many  cases  of  defilement  which  may  arise 
from  irregularities  in  the  site:  those  alone  will  be  discussed 
which  are  of  most  ordinary  occurrence,  and  which  rc(piirc 


240  INFLUENCE    OF    IRREGULARITIES    OF    SITE. 

for  tlit'ir  solution  the  usual  geometrical  constructions  in- 
volved in  tangent  and  secant  planes  and  other  surfaces,  to 
a  surface  detined  by  the  projection  of  its  horizontal  curves. 
The  cases  which  will  here  find  their  application  may  be 
arranged  under  two  heads:  1st,  the  plan  and  command  of 
a  work  being  definiteh'  decided  upon,  to  ascertain  the  exact 
portions  of  the  zones  of  danger  from  which  any  description 
of  fire  can  be  brought  to  bear  upon  its  terrepleins,  and  to 
defile  them  from  it;  2d,  the  plan  of  a  work  being  definitely 
fixed,  but  its  command  onh'  approximately  within  certain 
limits,  to  ascertain  the  easiest  method  of  defiling  the  terre- 
pleins of  the  work  by  varj'ing  the  command,  or  position 
of  the  interior  crest,  within  the  assigned  limits. 

71-3... Prob.  1,  Pl.  7,  Fig.  2.  The  command  or  posilion  of 
the  interior  crests  of  the  faces  of  a  loork  being  fxcd,  to  ascertain 
the  dangerous  looints  on  the  exterior,  and  to  defile  its  tcrreplein 
from  these  points. 

Let  ab,  ac,  be  the  projections  of  the  given  crest;  and  the 
curves  (28.0),  (29.0),  etc.,  those  of  the  natural  surface. 

Prolong  outward  to  c  and  d,  the  faces;  construct  the 
scales  of  declivity  of  the  two  lines  ae,  ad;  and,  fi-om  them, 
the  scale  of  declivity,  cf  of  their  plane.  From  the  salient 
a,  supposing  an  arc  to  be  described  with  a  radius  of  1,500 
yards,  the  dangerous  ground  will  be  included  between  it 
and  the  two  faces  of  the  work.  Now,  if  the  plane  of  the 
interior  crests,  of  which  ef  is  the  scale  of  declivity,  be 
indefinitely  extended,  and  its  intersection  with  the  surface 
parallel  to  the  natural  surface  and  6  feet  above  it  be  found, 
it  is  evident  that  the  portion  of  this  raised  surface  which 
lies  below  the  plane  may  be  disregarded,  as  no  fire  from  it 
can  have  a  plunge  u})on  the  interior  of  the  work.  But, 
from  every  point  of  the  surface  above  the  plane,  a  plunging 
fire  can  be  brought  to  bear  on  the  tcrreplein.  Having 
drawn  the  horizontals  of  the  plane  ef,  and  found  their 
intersections  with  the  corresponding  horizontals  of  the 
raised  surface  (which  last  will  be  given  by  adding  6  feet, 
or  2  yards,  to  the  references  of  the  curves  of  the  ground),  of 
which  xgz  is  the  projection.     That  portion  of  the  surface 


INFLUENCE  OF  IRREGULARITIES  OF  SITE.       241 

which  lies  above  this  curve  will  alone  have  a  plunging  fire 
upon  the  work,  and  will  be  the  oiily  poi'tion  tbi-  which 
defilement  will  be  necessary. 

Now,  as  this  intersection  falls  entirely  within  the  angle 
daeof  the  faces  prolonged,  or  Avitliin  the  limits  of  front 
fire,  it  is  evident  that  the  terrc[)leins  will  require  to  be 
defiled  (^nly  from  direct  fire. 

To  etiect  this,  let  a  }»Iane  be  passed  through  the  foce, 
bad,  of  the  work,  and  tangent  to  the  raised  surface  above 
xy  z.  This  [thine  will  ])ass  above  all  the  dangerous  ground, 
except  at  its  point  of  contact  with  it;  and,  being  extended 
back  from  the  face  within  the  work,  it  is  clear,  if  the  terre- 
plein  of  this  face  be  so  taken  with  respect  to  this  plane 
that  no  point  of  it  shall  be  less  than  8  feet  below  the  plane, 
that  then  eveiy  point  of  the  terreplein  will  be  screened 
from  a  plunging  fire  by  the  parapet  of  the  face  a  h.  Now, 
if  the  same  series  of  opei'ations  be  gone  through  with  for 
the  face  c  a  c,  then  will  its  terreplein  be  defiled  in  like 
manner;  and  thus  the  defilement  of  the  whole  work  be 
completed  for  this  case. 

The  tangent  planes  which  satisfy'  the  above  condition  are 
termed  Planes  of  Direct  Dejilcment,  and  they  may  be  defined 
as  planes  which,  jmssed  through  the  interior  crest  of  a  parapet, 
leave  at  least  Q  feet  below  them  all  the  dangerous  ground,  of  front 
fire,  and  pass  at  least  8  feet  above  every  point  of  the  terreplein 
behind  the  jMrapet. 

The  terrepleins  are  usually  parallel  to  their  res})ective 
planes  of  direct  defilement,  and  8  feet  below  them.  But 
when  the  declivity  of  the  })lane,  of  defilement  exceeds  .^^ , 
then  the  ti'rrejtlcin,  if  it  is  to  receive  cannon,  must  be  kept 
within  this  limit. 

In  the  Fig.  2,  the  relcrenccs  are  put  down  in  yards.  The 
tangent  plane  through  l)a<l  is  determined  in  the  usual 
manner,  by  finding  the  horizontal  (in  this  case  30,0), 
among  all  those  drawn  to  the  curves  of  the  raised  surface, 
which  makes  the  minimum  angle  with  bd.  The  line  A/, 
perpendicular  to  this  hori/ontah  is  the  scale  of  declivity  of 
this  plane;  and  the  jxtint  /;,  that  of  cotitact.  The  line  /.•  / 
IG 


242  INFLUENCE    OF    IRREGULARITIES    OF    SITE. 

is,  in  like  iii;iniior,  the  scale  of  deciixity  of  the  otlier  plane, 
and  0  its  })oint.of  eontaet. 

714. ..It  might  hapi)en,  frt)in  tlie  steepness  of  the  terre- 
pleins,  that  the  re-entering,  or  gutter,  formed  at  their  inter- 
section, would  be  inconvenient,  and  it  would,  therefore,  be 
desirable  to  have  this  portion  raised,  when  it  can  l)e  done 
without  exposure  to  a  plunging  iire.  This,  in  most  cases, 
ma\-  he  effected  in  this  way.  It  will  be  seen,  from  an 
inspection  of  the  Fig.  2,  that  the  points  o  and  p  arc  the 
only  ones  from  Avhich  the  enemy's  fire  passes  exactly  at  8 
feet  above  all  the  points  of  the  respective  terreplcins  deter- 
mined by  the  tangent  })lanes;  and  that  if,  from  these 
points,  lines  of  fire,  oar  and  jyas,  be  drawn,  every  other 
line  of  fire  through  a,  from  the  ground  in  the  angle  pao, 
will  pass  more  than  8  feet  above  the  portion  of  the  terre- 
plcins embraced  in  the  angle  sai\  since  the  ground  within 
the  exterior  angle  lies  below  the  tangent  planes.  If,  then, 
a  bo  taken  as  the  vertex  of  a  cone,  the  elements  of  whicli 
are  tangent  to  the  raised  sui'face  within  the  angle  pao,  and 
if  these  elements  be  prolonged  within  the  woi'k,  their  pro- 
longation will  form  a  cone  of  lines  of  fire,  which  will  pass 
more  than  8  feet  above  the  terrepleins.  If  these  last,  there- 
fore, be  connected  by  a  surface  parallel  to  this  cone,  and  8 
feet  below  it,  this  surface  may  be  taken  as  the  portion  of 
the  terreplein  which,  connecting  the  two  plane  portions, 
will   remedy  the  inconvenience  pointed  out. 

7ir)...PK0B.  2,  Fig.  3.  The  data  bemg  the  same  as  in  the 
preceding  case,  a.nd  the  work  being  exposed,  to  both  direct  and 
reverse  views,  to  cover  its  interior  from  these  views. 

Suppose  the  plane  of  the  interior  crest  of  the  faces  ex- 
tended within  the  limits,  and  its  intersection  with  the 
dangerous  ground  determined,  as  in  the  preceding  case; 
and  let  x  y  z,  rn  n  o  and  p  q  r  be  the  curves  of  this  inter- 
section. 

The  face  ab  Avill  be  exposed  to  direct  fire  alone  from  the 
ground  above  the  two  curves,  x  y  z  and  mno,  and  to  reverse 
fire  from  that  above  the  curve  pqr.  In  like  manner,  the 
face  ac  will  be  exposed  to  direct  fire  from  xyz  and  pqr, 
and  to  reverse  fire  from  m  n  o. 


INFLUENCE    OF    I1UIE(UTLAR1TIES    OF    8ITE.  243 

The  defilement  of  each  tkce,  from  the  direct  fire,  will  be 
eftected  precisely  in  the  same  Avay  as  in  the  preceding 
problem.  The  lines  hi  and  hi  are  the  scales  of  declivity  of 
the  planes  of  direct  defilement  of  the  faces  respectively. 

For  the  reverse  defilement,  a  plane  is  passed  through  a  6, 
tangent  to  the  surface  above  pqr;  and  one  through  a<?, 
tangent  to  the  surface  al)ove  vino,  and  their  line  of  inter- 
section aa'  found.  The  line  iiv  is  the  scale  of  declivity  of 
one  of  these  planes,  termed  a  Plane  of  Reverse  Deji/e)ne?it, 
and  6;  t  that  of  the  other. 

Now,  if  a  traverse  is  so  placed  that  its  crest  shall  occupy 
the  position  of  the  line  a  a/,  it  will  cover  all  between  it 
and  the  two  faces,  as  high  as  the  interior  crests,  from  the 
reverse  fire  on  each  side.  But  as  it  is  desirable  to  have  the 
troops,  when  on  the  banquettes,  screened  from  this  fire, 
the  crest  of  the  traverse  should  be  raised  from  18  inches  to 
2  feet  above  the  line  a  a',  to  eftect  this. 

The  traverse  should  extend  so  far  toward  the  gorge  of 
the  work  that  the  entire  line  of  each  face  shall  be  covered 
by  it.  To  determine  its  length  with  this  condition,  lines 
are  drawn  from  the  extreme  })oint,  h  and  r,  of  the  faces, 
tangent  to  the  curves  )iino  and  ])'j)\  and  their  points  ot 
intersection  with  a  a'  marked;  the  one  that  falls  farthest 
from  the  salient,  will  evidently  give  the  required  length. 

If  the  line  a  a'  should  I'all  so  near  eitlier  of  the  faces  that 
the  traverse,  if  placed  along  it,  would  incommode  the  ser- 
vice of  that  part  of  the  work,  it  will  be  best  to  place  itH 
crest  in  the  vertical  plane  a  a"  of  the  capital  of  the  work. 
When  80  placed,  the  intersection  of  this  vertical  plane  with 
each  of  the  planes  of  reverse  defilement  must  be  found, 
and  the  crest  of  the  traverse  be  taken  18  inches  above  tlie 
one  that  lies  highest. 

71(>...Tlic  ]>osition  of  the  crest  of  the  traverse,  as  deter- 
mined by  either  of  the  preceding  methods,  will  be  in  a 
vertical  plane  passing  through  the  salient  a  of  the  work. 
From  the  thickness  and  slopes  which  traverses  usually 
receive,  they  would  ordinarily,  if  placed  in  this  position, 
take  up  all  the  interior  space  within  the  salient,  and  leave 


244  INFLUENCE    OF    IRREGULARITIES    OF   SITE. 

no  room  there  for  dispositions  eitlier  for  artillery  or  mus- 
ketry. To  prevent  this,  a  break  is  made  in  the  direction  of 
the  crest,  at  some  point  on  tlie  vertical  plane  through  the 
salient,  from  which  it  is  directed  on  a  point  of  either  of  the 
faces,  so  far  from  the  salient  that  sntHcient  room  will  he 
left  for  the  object  in  view.  In  the  Fig.  4,  which  illustrates 
this  arrangement,  the  traverse  is  withdrawn  far  enough 
from  the  salient  to  leave  room  for  a  barbette  battery  for 
several  guns. 

The  face  upon  Avhich  the  traverse  is  directed,  will  l)e 
determined  by  the  condition  of  covering  both  faces  in  the 
most  effective  manner,  by  the  position  taken  for  the 
traverse. 

7 17... The  cross  section  of  traverses  for  permanent  works 
is  similar  to  those  used  in  field-works.  The  top  of  the 
traverse  receives  a  slight  slope  each  way  from  the  crest  to 
the  sides.  The  thickness  at  top  is  from  12  to  20  feet,  to 
render  it  shot-proof.  The  sides  take  the  natural  slope  from 
the  top,  either  to  their  intersections  with  the  planes  of 
direct  defilement  or  to  the  terreplein.  If,  to  gain  interior 
space,  these  slopes  are  terminated  at  the  planes  of  direct 
defilement,  then  the  portions  of  the  traverse  below  these 
planes  are  made  more  steep,  and  the  earth  supported  by 
retaining  walls.  The  top  of  the  traverse,  where  it  joins  the 
parapet,  being  higher  than  the  superior  slope,  is  run  out 
above  this  slope,  ui)on  which  the  side  slopes  fall  ;  its 
extremity  terminates  in  the  plane  of  the  exterior  slope, 
extended  above  the  exterior  crest. 

718... Traverses  may  be  arranged  for  bomb-proof  shelters 
and  musketry  defence,  by  throwing  a  bomb-proof  arch 
between  the  side  retaining  walls,  and  piercing  the  Avail 
bearing  on  the  portion  of  the  terreplein  which  will  first  fall 
into  the  enemy's  power  with  loop-holes. 

719...AV^hen,  from  any  circumstance,  a  single  traverse 
cannot  be  used  for  reverse  defilement,  resort  must  be  had 
to  several,  which  should  be  so  combined  that  no  line  of  fire 
can  })enctrate  between  their  extremities  to  attain  any  point 
which  they  should  cover.     The  examples  of  like  combina- 


INFLUENCE    OF    IRREGULARITIES    OF    SITE.  245 

ti(Mis  given  in  the  Front,  will  readily  suggest  the  manner  of 
making  others;  ot"  ■which  farther  illustrations  will  he  found 
in  the  following  case. 

720... Where  a  demilune  is  arranged  with  a  redouht,  a 
traverse  placed  in  its  salient  cannot  he  extended  farther 
back  than  the  counterscarp  of  the  redoubt,  and  an  open 
space,  therefore,  will  l)e  left  at  the  ditch,  through  which  a 
reverse  fire  would  attain  that  portion  of  cither  face  which 
is  not  covered  either  b}'  the  traverse  in  the  salient  or  by 
the  parapet  of  the  redoubt.  To  cover  the  part  thus  ex- 
lK)sed.  it  will  be  necessary  to  place  one  or  more  traverses 
which,  in  combination  with  the  one  in  the  salient  and  the 
para[iet  of  the  redoubt,  shall  subserve  this  ench 

To  simplify  the  case,  let  the  face  ac,  PI.  7,  Fig.  5,  be  the 
one  exposed,  ami  let  the  point  x  be  one  the  lire  of  which  is 
most  dangerous.  Having,  in  tlie  first  place,  arranged  the 
traverse  /,  as  in  the  last  example,  and  drawn  the  two  lines 
of  fire,  xb  and  xd.,  from  the  point  x,  through  the  extremity 
of  the  traverse  and  the  top  of  the  parapet  of  the  redoubt 
at  the  salient,  the  length,  hd,  of  the  face  intercepted  between 
these  lines  will  be  the  part  to  be  covered.  If  a  second  trav- 
erse, /',  be  itlaced  across  the  terreplein  of  the  other  face  of 
the  demilune,  and  in  a  position  such  that  one  of  its  ends 
shall  rest  on  xh,  and  the  other  on  x  d,  it  will  evidently 
cover  the  portion  bd. 

721. ..In  selecting  the  positions  of  several  combined  trav- 
erses, attention  must  be  given  to  avoid  those  where,  if  one 
be  placed,  the  enemy  would  find  shelter  behind  it  from  the 
tire  in  the  rear.  In  the  example  just  taken,  the  slope  of  i, 
toward  the  salient,  should  be  swept  by  the  fire  from  the 
rear,  through  the  redoubt  ditch  ;  the  like  slope  of  t'  should 
be  swejtt  by  a  portion  of  the  redoubt  face  near  its  salient; 
and  neither  so  fall  as  to  have  the  space  l^ehind  it  masked 
from  fire  by  the  one  to  its  rear. 

722... Traverses  usuall}'  present  not  only  the  easiest  solu- 
tion of  all  problems  of  reverse  and  enfilading  di'filement, 
but,  affording  the  means  of  rendci'ing  the  command  inde- 
pendent of  the  fire  from  without,  they  enable  the  engiiicer 


246  iMi,ri:x(M-:  of  iiiui:(;uLARTTrEs  of  sitr. 

to  ros^nlate  this  element  solely  with  a  view  to  the  (^fteet 
which  he  desires  to  attain  hv  his  own  Hre.  From  the  s])aee 
recjuired  for  their  erection,  traverses  may,  as  in  the  cases  of 
narrow  terrepleins,  like  those  of  the  covered-ways,  and  of 
the  demilune  with  a  redoul)t,  he  inconvenient,  both  from 
eml)arrassing  the  communications  and  from  taking  up 
ground  that  may  be  wanted  for  batteries. 

723...Prob.  3.  The  plan  of  a  bastion  hcing  definitiveli/  Jixed, 
and  one  point  of  its  command  approximately^  to  defile  the  work 
in  the  most  advantageous  manner^  hj  shiffinq  the  jw-'fition  of  its 
interior  crest  within  certain  limits. 

Let  Fig.  6  be  the  plan  of  the  work,  and  a  the  salient, 
the  command  of  which  can  be  varied  within  certain  limits, 
without  impairing  any  of  the  other  conditions;  and  let  the 
dangerous  ground  be  embraced  within  the  arc  nin,  at  1,500 
yards  from  rt,  and  the  lines  an  and  av  supposed  drawn 
from  a.,  through  covering  masses  on  the  right  and  left  of 
the  work. 

The  front  limits  of  defilement  in  this  case  are  eml>raced 
within  the  sector  man;  and  the  lateral  limits  within  the 
other  two,  mau  and  n  a  v.  Now',  the  most  favoral)le  case  of 
deiilement  liere  will  be  that,  wliere  a  plane,  containing  a 
taken  within  its  extreme  positions,  shall  })ass  above  all  the 
exterior  ground,  and  give  such  a  command  to  the  interior 
crest  throughout,  when  held  in  it,  as  shall  satisfy  the  other 
conditions  of  defence.  To  ascertain  the  existence  of  such 
a  plane,  let  a  be  taken  as  the  vertex  of  a  cone  which  envel- 
ops all  the  dangerous  ground,  any  plane  tangent  {o  this 
cone  will  satisfy  the  condition  of  defilement,  and  it  will, 
therefore,  only  be  necessary  to  find  whether  any  one  of 
these  planes  of  defilement  will  satisfy  the  other,  of  giving 
the  points  h,  c,  <l  and  e  a  suitable  command.  If  no  such 
plane  can  be  obtained,  the  next  most  favorable  case  will  be 
to  find  one  that  shall  satisf^y  all  the  recpiisite  conditions  of 
comiiiaiid,  and  intci-scct  the  ground  only  within  the  front 
limits.  In  this  case  it  is  clear,  frtun  the  position  of  this 
plane,  if  the  interior  crests  are  held  in  it,  that  the  interior 


INFLUENCE    OF    IRRE(;ULAIIITIE8    OF    SITE.  247 

of  the  work  will  be  exposed  only  to  the  direct  fire  from 
that  portion  of  the  fi:ronnd  which  lies  above  the  ])lane. 

Let  xy  z  be  the  curve  of  intersection  of  the  phine  with 
the  ground,  found  in  the  usual  way.  Through  the  faces 
ab  and  ad,  let  ]»lancs  of  direct  defilement  be  passed;  the 
terrc[)Icins  of  the  faces  being  held  parallel  to  them  will  be 
covered  by  their  respective  para})cts  from  all  plunging  fire. 
But,  in  order  that  the  planes  of  defilement  of  the  faces 
shall  also  defile  tlie  flanks,  it  is  necessary  that  each  flank 
be  placed  in  the  plane  of  defilement  of  the  adjacent  face, 
and  its  terreplein  in  that  of  the  terreplein  of  the  face. 
Xow,  in  giving  the  interior  crests  of  the  flanks  tliese  new 
positions,  they  will  lie  below  the  plane  that  contains  the 
curve  x]i z,  and  in  whicli  the  interior  crests  of  the  faces  lie. 
Tliis  being  the  case,  it  ma}-  happen  that  the  parapet  of  one 
of  the  flanks  will  not  cover  the  opposite  face  from  reverse 
fire,  coming  from  the  lateral  limits  opposite  the  flank.  In 
this  contingency  it  will  be  necessar}-,  in  order  to  cover  the 
face,  to  place  the  flank  in  the  plane  of  the  curve  x y  z^  as 
this  plane  defiles  from  the  lateral  limits;  but,  in  doing  this, 
the  flank  de,  for  example,  will  be  exposed,  in  its  turn,  to 
tlie  ground  above  xy  z ;  and  to  cover  it,  the  only  remedy  is 
to  erect  a  traverse,  at  some  suitable  point,  which  shall  inter- 
cept all  this  dangerous  fire.  The  least  inconvenient  posi- 
tion for  the  traverse  will  usuall}^  be  at  the  shoulder  angle. 
From  this  point,  it  must  extend  so  far  l)ack  as  to  intercept 
all  fire  from  above  xyz^  both  on  the  terrcplcins  of  the 
flank  and  curtain,  where  they  unite,  and  he  high  enough 
to  screen  the  troops  on  the  banquette. 

If  the  defilement  cannot  be  eftected  by  eitlier  of  these 
processes,  there  remains  no  other  means  than,  having  first 
definitely  fixed  the  command,  to  divide  the  bastion  liy  a 
traverse,  either  along  its  ca[>ital  or  some  other  convenient 
direction,  and,  liaving  given  it  a  suitable  lieiglit,  to  cover 
each  portion  from  direct  fire  by  tlie  usual  method. 

724. ..The  foregoing  problems  embrace  in  their  solution 
all  of  the  more  ordinary  cases  of  defilement,  and  suggest 
the  route  to  be  followed  in  treatinir  others.     In  all  cases  of 


248  INFLUENCE    OF    IRREGULARITIES    OF    SITE. 

the  dclilemeiit  of  combined  works,  like  the  enceinte  and 
its  outworks,  etc.,  it  must  be  borne  in  mind  that  the  ad- 
vanced works^which,  from  their  position,  must  first  fall  into 
the  enemy's  power,  become  thus  a  portion  of  the  danger- 
ous ground  for  the  works  more  retired,  and  which  must 
also  be  held  after  the  fall  of  the  others.  The  retired  works, 
under  sucli  circumstances,  must  be  defiled  from  the  ad- 
vanced ;  their  planes  of  defilement  being  made  to  pass  from 
3  feet  to  4.5  feet  above  the  portion  of  the  advanced  work 
on  which  it  is  presumed  the  enemy  may  make  a  lodgment, 
and  which,  from  its  position,  may  be  regarded  as  tlie  most 
dangerous  to  the  retired  work.  It  is  according  to  this  rule 
that  the  redoubt  of  the  re-entering  place  of  arms  is  defiled 
from  the  parapets  of  the  two  adjacent  demilunes;  its  plane 
of  defilement  extended  outward,  passing  at  3  feet  above  the 
salients  of  these  works.  The  tenaille,  in  like  manner,  is 
defiled  from  the  upper  terreplein  of  the  demilune  redoubt, 
as  the  tenaille  must  be  held  after  the  enemy  has  established 
himself  on  this  terreplein.  For  like  reasons,  the  more 
retii'cd  portions  of  the  covered-ways  are  defiled  from  the 
enemy's  lodgments  on  the  glacis  of  the  demilune  salient 
place  of  arms. 

725... Where  a  work  has  considerable  command,  and  is 
open  at  the  gorge,  like  the  cavalier  retrenchments,  for 
example,  and  the  works  in  its  rear  do  not  mask  its  in- 
terior from  reverse  fire,  it  may  be  necessar}^  to  place  the 
traverse,  termed  a  'parados^  across  its  terreplein  at  the 
irorire,  irivins:  it  sufiEicient  heio-ht  to  subserve  the  end  in 
view. 

72(3... The  methods  of  defilement  here  laid  down  are 
those  now  followed  by  engineers.  They  unite  mathemati- 
cal accuracy  in  results,  with  great  simplicity  of  detail ; 
and  render  the  defilement  altogether  secondary  to  the 
other  conditions  of  defence,  upon  which  the  plan  and 
command  are  made  essentially  to  depend.  Before  they 
were  adopted,  the  results  of  the  method  then  followed 
were,  in  most  respects,  like  those  obtained  in  the  prac- 
tical oi)erations  for  defiling  field-works.     A  line,  the  posi- 


INFLUENCE    OF    IRREGULARITIES    OF    SITE.  249 

tioii  of  wliicli  was  tlctcniiined  by  a  scries  of  trials,  having 
for  tlicir  object  to  obtain  the  most  satisfactory  results,  both 
as  to  the  economy  of  the  requisite  embankments  and  the 
best  disposition  of  command  of  the  various  parts  at  or  in 
rear  of  the  gorge  of  the  work  to  be  defiled  ;  this  position 
coinciding  with  the  natural  surface,  or  being  above  or 
beneath  it,  as  the  case  required.  Through  this  line  a 
plane  was  passed  tangent  to  the  dangerous  ground.  This 
plane,  termed,  as  in  tield  defilement,  a  Rampant  Plane,  was 
taken  as  the  artificial  site  of  the  work,  in  reference  to 
Avliich  the  relative  command  of  all  the  parts  was  arranged 
as  upon  a  horizontal  site.  Or,  in  other  words,  the  result 
was  nearly  the  same  as  if  the  A\<>rks  had  been  arranged  on 
a  hoi'izontal  site,  and  then  the  whole  combination  turned 
around  some  fixed  line  of  this  site,  until  it  was  l)rought 
into  the  position  of  the  retpiired  rampant  plane.  The 
defects  of  this  method  are  evident  at  a  glance.  It  pre- 
serves the  relations  of  defence  of  the  various  works  the 
same  as  in  a  liorizontal  site ;  but  it,  to  a  great  extent, 
leaves  out  of  consideration  the  bearing  of  the  command 
on  the  exterior  ground,  and,  in  many  cases,  ma}'  lead  to 
excessive  excavations  and  eml)ankments  which  tlic  meth- 
ods now  followed  enable  the  engineer,  for  the  most  part,  to 
avoid. 

727...1\HMARKS.  In  the  preceding  discussions  it  will  be 
observed  that  the  limits  of  defilement,  horizontally,  have 
been  based  upon  the  range  and  presumed  accurac}'  of  fire 
of  artillery  and  small  arms  before  the  changes  which, 
within  a  few  years  back,  have  taken  place  in  both  these 
particulars,  and  which  —  from  the  zeal  and  intelligence 
with  which  exi)eriments  are  now  being  carried  on,  in 
every  part  of  the  civilized  world,  on  the  forms  of  cannon 
and  ]>rojectiles  and  the  quality  of  powder  —  will,  in  all 
probability,  be  extended  and  lead  to  still  more  remark- 
able results.  These  imi)rovements,  however,  will  have 
no  other  effect  U[><)n  the  rules  and  modes  of  defilement 
now  in  use  than  to  change  the  limits,  horizotiUdhi,  to  cor- 


250  MINES. 

respond  with  the  increased  ranges  of  projectiles.  So  far 
as  an  iniprovenient  in  the  accuracy  of  fire  is  concerned,  it 
will  render  a  strict  defilement  of  all  parts  of  the  interior  of 
a  work  more  imperative,  and  will  lead  engineers  to  resort 
to  ev^ery  means  by  which  the  troops  and  materiel  can  be 
hidden  from  an  enemy's  view  within  the  extreme  range  of 
projectiles.  As  to  the  vertical  limits,  there  would  seem  to 
be  no  good  reason  for  changing  those  now  established. 
When  it  is,  also,  taken  into  consideration  that  the  rela- 
tive command  and  plunge  of  heights  decrease  with  their 
distance  from  the  work  defiled,  and,  also,  that  the  accuracy 
of  aim  is  greatly  affected  by  the  same  cause,  it  is  ques- 
tionable whether  any  considerable  extension  of  the  limits 
hitherto  laid  down  will  be  necessarj",  except  in  marked 
cases  of  locality. 


[ine.^. 


728... The  subject  of  mines  admits  of  a  division  into  five 
parts  : 

1st.  The  nomenclature. 

2d.  The  results  of  experiments,  and  the  theory  founded 
on  them. 

3d.  The  manner  of  using  mines  in  the  attack  and 
defence. 

4th.  The  conditions  to  which  mines  should  be  subjected 
in  their  arrangement  and  uses. 

5th.  The  construction  or  details  of  the  practical  opera- 
tions. 

To  these  may  be  added  a  sixth  part,  comprising  the  uses 
of  mines  in  temporary  works. 


MINES.  251 

729...]SroMENCLATURE.  Tlic  tcrm  mine  is  applied  l)oth  to 
tlie  undcrgrouii<]  excavations  charged  with  powder  for  the 
purpose  of  producing  an  external  explosion,  and  to  the 
communications  which  lead  to  these  excavations. 

The  excavation  in  which  the  charge  of  powder  is  lodged 
is  termed  the  chimbcr.  The  pit  formed  hy  the  explosion  is 
termed  the  crafcr. 

The  form  of  the  crater  in  ordinary  soils  has  not  been 
exactly  ascertained.  The  only  use  of  the  exact  determina- 
tion of  this  form  would  he  to  calculate  precisely  the  quan- 
tity of  earth  thrown  from  the  crater,  and  by  that  means  to 
proportion  the  charge  to  the  effect  to  be  produced.  Dif- 
ferent figures  have  been  assigned  by  engineers  to  this 
solid;  some  assuming  it  to  be  a  cone,  of  Avhich  the  cen- 
tre of  the  powder  was  taken  as  the  vertex  ;  others,  a 
paraboloid,  of  which  the  centre  of  the  powder  was  the 
focus.  To  afford  a  uniform  and  simple  rule  for  calculat- 
ing the  volume  of  the  crater,  the  solid,  Fig.  A,  is  assumed 
to  be  a  truncated  cone,  the  radius,  o  d^  of  the  lower  circle 

Si  s  \)  being  one-half  the  radius,  j)  h,  of 

^^^__^-___^___^.____.,.,  ^^^^  upper  circle.    The  radius,  2>  l>, 

^^ic     ''^''iiiw  ^^  *^^^  upper  circle  is  termed  the 

'W^^^^W  crater  radius.    The  line,  op,  drawn 

'nI-''  from    the    centre    of  the   powder 

ri?-  A.  perpendicular  to  the  surface  where 

the  explosion  takes  place,  the  Hue  of  least  resistance.  The 
line,  ob,  drawn  from  the  same  centre  to  any  point  in  the 
circumference  of  the  upper  circle,  the  radius  of  cxplosivti. 
The  term  common  mine  is  applied  to  a  crater  when  its 
radius  is  equal  to  the  line  of  least  resistance.  When  the 
crater  radius  is  greater  than  the  line  of  least  resistance,  the 
terms  occrcharr/ed  mine  and  globe  of  compression  are  used. 
Wlien  the  crater  radius  is  less  than  the  line  of  least  re- 
sistance, the  mine  is  termed  undercharged.  A  small  mine 
with  a  line  of  least  resistance  not  greater  than  9  feet,  which 
is  formed  by  sinking  a  shaft  from  the  surface  of  the  grouml, 
is  termed  a  fougassc.      The   term    camoufiei  is  applied  to 


252  MINES. 

small  mines  used  to  siiftbcate  the  enem3''s  miner  without 
producing  an  external  explosion. 

The  underground  communications  required  for  the  ser- 
vice of  mines  are  termed  galleries.  Tlie  galleries  are  either 
arched  communications  of  masonry,  or  else  a  framework 
and  sheeting  of  timber.  The  principal  gallerj^  immediately 
behind  the  counterscarp  wall,  is  termed  the  counterscarp  or 
magistral  gallery.  An  enveloping  gallery  is  one  parallel  to  the 
counterscarp  galler}'^,  and  at  some  30  or  40  yards  in  advance 
of  it.  The  galleries  leading  outward  from  the  counter- 
scarp gallery  are  termed  listening  galleries.  The  galleries 
which  connect  several  listening  galleries  are  termed  trans- 
versal or  cross  galleries.  Galleries  receive,  also,  particular 
names  from  their  size,  as  the 

Great  or  grand  galleries,  which  are  6  feet  high  and  6  feet  wide. 
Common  galleries,  "        G        "  "3       " 

Half  galleries,  "        ^      "  "    3       " 

Branches,  "        ^      "  "    2i     " 

Small  branches,  "        2i      "  "    2       " 

730... Experiments.  But  little  advance  by  experiment 
has  been  made  in  the  subject  of  mines,  owing  to  the  time, 
labor  and  expense,  which  a  prosecution  of  the  subject 
demands;  and  the  practice  has,  therefore,  undergone  but 
slight  changes  since  the  earliest  introduction  of  this  means 
of  attack  and  defence.  The  following  facts,  drawn  from 
observation,  comprise  almost  all  that  is  at  present  known 
on  the  subject: 

1st.  In  solid  rock,  an  explosion  causes  the  rock  to  split 
in  various  directions,  and  if  the  charge  is  heavy,,  will  break 
it  into  small  fragments,  which  are  frequently  thrown  to  a 
great  distance. 

2d.  In  sand,  the  gazes  seem  to  penetrate  between  the 
grains,  producing  a  crater  of  a  regular  form,  the  radius  of 
the  upper  circle  of  which  is  generally  small  in  comparison 
with  the  depth. 

3d.  In  ordinary  tenacious  soils,  the  first  e'fiect  of  the 
explosion  is  to  produce  a  rumbling  noise,  and  a  sensible 


MINES.  253 

trembling  of  the  earth  aroniid  the  mine  to  a  considerable 
distance;  the  gronnd  directly  over  the  mine  is  next  ob- 
served to  rise  in  the  form  of  a  spherical  segment,  wliich 
increases  perceptibly  nntil  the  smoke  commences  to  issue 
forth  around  its  base.;  the  explosion  outward  follows  imme- 
diately on  this  last  change,  the  earth,  mingled  with  smoke 
and  flame,  being  thrown  upward  and  outward,  so  as  to 
assume  a  form  something  like  a  water-spout;  part  of  the 
earth  falling  back  into  the  crater  and  a  part  without,  form- 
ing a  ridge  around  its  month. 

The  two  most  remarkable  features  of  the  explosion  are 
its  internal  and  external  effects;  the  flrst  producing  the 
crater,  the  second  so  disturbing  the  earth  for  a  consider- 
able distance  around  the  crater  as  to  fill  up  cavities,  destroy 
galleries,  etc.,  within  the  sphere  of  its  action  ;  these  effects 
extending  farther  in  a  lateral  than  in  a  downward  direction. 
The  charges  and  their  effects  do  not  follow  the  same 
ratio,  the  last  increasing  less  rapidly  than  the  first.  Experi- 
ment has  shown  that  the  charges  may  even  be  increased 
one  or  two  pounds  per  4  cubic  yards,  without  increasing 
the  crater  radius;  the  only  effect  of  this  increase  of  charge 
being  to  throw  more  of  the  earth  clear  of  the  crater. 

From  experiments  made  on  common  mines,  with  a  line 
of  least  resistance  not  exceeding  15  feet,  it  has  been  ascer- 
tained that  the  tenacity  of  the  earth  is  completely  destroyed 
around  the  crater,  to  a  distance  equal  to  the  line  of  least 
resistance,  and  that  empty  galleries  are  broken  in  at  a  dis- 
tance of  one  and  a  half  the  same  line. 

In  homogeneous  soils,  the  resistance  due  to  the  tenacity 
of  the  soil  Is  nearly  proportional  to  the  mass. 

It  was  for  a  long  time  supposed  by  miners  that  a  crater 
could  not  be  formed  with  a  diameter  greater  than  twice  the 
line  of  least  resistance,  with  any  charge;  but  the  experi- 
ments of  Bclidor  have  shown  that,  by  successive  augmenta- 
tions of  the  charge,  the  crater  radius  may  be  increased  to 
six  times  this  line,  but  not  much  beyond;  that  within  this 
limit  the  ratio  of  the  diameters  of  the  craters  is  nearly  that 


254  MINES. 

of  the  square  root  of  the  charges;  and  that  galleries  can  be 
destroyed  by  such  miues  at  distances  of  four  times  their 
line  of  least  resistance. 

731. ..Theory.  The  physico- mathematical  theory  of 
mines  is  still  very  imperfect,  owing  to  the  impracticability 
of  ascertaining  the  exact  effects  of  the  explosion  of  powder 
in  a  medium  which  is  seldom  homogeneous,  and  the  resist- 
ance of  which,  arising  from  its  tenacity,  compressibility, 
etc.,  to  the  expansion  of  the  gazes,  can  only  be  arrived  at 
by  a  wide  range  of  experiments  made  with  minute  care. 

From  the  want  of  these  elementary  data,  the  formula  at 
present  in  use,  to  determine  the  charges  for  different  media, 
are  necessarily'  empirical,  and  their  results  are  to  be  relied 
on  only  within  the  limits  in  wdiich  they  coincide  with 
experiments.  For  most  cases  in  practice,  these  approxi- 
mations are  near  enough,  and  valuable  as  the  only  guides 
that  the  miner  has  to  refer  to. 

732... The  resistances  which  the  gazes  overcome  are  the 
weight  of  the  volume  of  earth  thrown  from  the  crater,  the 
tenacity  of  the  medium,  and  the  atmospheric  pressure  on 
the  upper  circle  of  the  crater.  The  two  first  are  pro- 
portional to  the  mass  of  earth  thrown  out,  and  the  last  to 
the  upper  surfiice  of  the  crater.  To  express  the  ratio  of 
these  resistances  to  the  charges,  let  us  represent  in  any  two 
mines  by 

c  c',  the  charges  ; 

rr',  the  radii  of  the  craters; 

I  U,  the  lines  of  least  resistance  ; 

d  d'^  the  weight  of  the  unit  of  volume  of  the  two  soils ; 

n  n',  the  constants,  which,  multiplied  into  the  weights, 
will  express  the  tenacities  ; 

h  A',  the  heights  of  the  atmospheric  columns  reduced  to 
the  densities  as  the  soils. 

Whatever  may  be  the  form  of  the  crater,  its  volume  can 
be  expressed  in  terms  of  the  surface  of  the  upper  circle, 
and  some  fractional  part  of  the  line  of  least  resistance;  so 
that  if  we  represent  by  -  I  and  -,  I'  this  fractional'  part  of 


MINKS.  255 

the  line  of  least  resistance  in  the  two  cases,  we  shall  have 
for  the  expression  of  the  two  volumes : 

■jr?- -  X-,  and  TT?-'-  X  -; 
and  for  their  respective  weights, 

m  m' 

to  express  the  tenacities  we  have, 

"l^^Xn,  and  ^il^Xn'; 
"1  7/1/ 

and    for  the  weights    corresponding    to    the    atmospheric 

pressures, 

'rri-'^hd,  and  -rrr'-^/t'd'. 

From  these  expressions  we  ohtain  the  proportions 

For  the  same  soil,  as  m^^^m',  n^n',  d-^d',  and  h  =  h',  this 
proportion  hecomes 

.:o'::r^(H-,,^i/.):'--'(n  ,;■",*'). 

733... The  relation  hetween  any  two  charges  of  mines  in 
the  same  soil,  ex])resse(l  hy  this  proportion,  gives  the  means 
of  ohtaining  the  charge  for  any  crater  when,  by  experi- 
ment, the  crater  formed  by  any  known  charge  has  been 
found,  provided  the  quantities  n  and  /i  are  known.  Of  the 
tirst,  nothing  definite  is  known  but  that  it  varies  Avith 
the  kind  of  soil.  The  second  has  been  assumed  equal  to 
11  feet.  This  want  of  definiteness  in  the  value  of  these 
quantitie-s  has  led  to  omitting  them  in  the  proportion, 
when  used  for  practical  purposes,  in  which  case  it  takes 
the  following  form  : 

c.  c'y.lr'^ :  I'  r'l 

This  is  termed  the  Miner's  Ride,  as  it  is  used  for  calculat- 
ing tables  of  charges  for  different  soils;  and  its  results  do 
not  differ  materially  from  those  of  experiments. 

Making  l^l',  the  proportion  becomes 
(' :  c' : :  r  ^ :  r'  ^, 
a  proportion  also  differing  but  little  from  the  results  ob- 
tained within  the  ordinary  limits  of  practice,  when   the 
lines  of  least  resistance  are  the  same  for  different  charges. 


256  MINES. 

734. ..Assuming,  as  is  the  case  in  common  mines,  tliat 
the  craters  are  similar  solids,  then  I :  I' '.'.  r  '.  r' ;  hence, 

c:  c'y.P:  V\ 
another  form  of  the  Miner's  Rnle,  and  the  one  used  in  cal- 
culating the  tahles  of  charges  for  similar  mines. 

The  manner  in  which  this  rule  is  applied  to  calculate 
charges  of  common  mines  is  as  follows  :  the  (quantity  of 
powder,  q,  in  pounds,  required  to  throw  up  one  cuhic  yard 
of  any  species  of  soil,  is  found  by  experiment.  As  the  solid 
contents  of  a  truncated  cone,  like  Fig.  A,  is  equal  to  y  P,  I 
being  the  line  of  least  resistance,  the  volume  of  the  crater, 
whose  line  of  least  resistance  is  one  yard,  will  be  repre- 
sented by  VX(l^)  or  V  ;  this  volume,  nmltiplied  by  q,  will 
give  the  charge  in  pounds  for  this  crater,  but  from  the  pro- 
portion c  :  c'::  P  :  l'^,  there  obtains: 

c:  V?::-^':l',  orc  =  V  ^^', 
for  the  charge  for  a  crater  whose  line  of  least  resistance 

is  l.  To  find  the  charge,  therefore,  for  a  given  line  of  least  resist- 
ance, cube  this  line,  exj^ressed  in  yards;  take  V  of  the  result  and 
multiplg  it  bg  the  number  of  pounds  required,  to  throw  out  a  cubic 
yard  of  the  soil  in  question. 

The  following  table  expresses  the  values  of  q: 

Ll)s.     0/.. 

Light  sandy  earth  1     13 

Hard  sand 2     00 

Common  earth 1     10 

Wet  sand :  2       2 

Earth  mixed  with  pebbles 2       8 

Clay  mixed  with  loam 2       8 

Rock 3     10 

735. ..As  the  Miner's  Rule  is  applicable  only  to  common 
mines,  resort  must  be  had  to  some  other  to  find  the  charges 
for  overcharged  and  undercharged  mines.  The  formula  in 
most  general  use  for  these  cases  are  those  of  Lebrun,  a 
French  engineer ;  wdiich,  although  not  based  on  any  satis- 
factory hypothesis,  nevertheless,  coincide  nearly  in  their 
results  with  those  obtained  by  experiments  within  ordinary 
limits.     The  hypothesis  assumed  to  obtain  these  formula  is 


MINES.  257 

as  follows :  Suppose  two  craters,  formed  hy  two  different 
charges,  c  and  c',  with  the  same  line  of  least  resistance,  one 
giving  a  crater  radius,  r,  equal  to  the  line  of  least  resist- 
ance, the  other  a  crater  radius,  7?,  greater,  the  difference  of 
the  radii  being  7? — r.  Next,  suppose  the  charge  c'  to  belong 
to  a  common  mine,  of  which  the  crater  radius  is  r;  r' — r, 
being  the  difference  of  the  radii  of  two  craters  of  the  com- 
mon mines  of  which  the  charges  are  c  and  c' ;  then  the 
ratio  of  the  two  differences  here  expressed,  arising  from 
the  same  increase,  c',  of  the  charge  c,  will  be  constant 
under  all  circumstances  of  variation  of  soil,  and  of  the  lines 
of  least  resistance.  Calling  K  this  constant  ratio,  there 
obtains  : 

'^  =  K; 

r  —  r  ' 

assuming  R^=nr,  this  formula  becomes 

r' r  '. 

but  as  r'  and  r  belong  to  similar  craters,  the  Miner's  Rule 
gives  -  =  ~;  from  this  there  obtains, 

c'  r'  ■* 

The  quantity,  /i,  which  enters  into  this  expression  must 
be  ascertained  by  experiment,  as  indicated  by  the  process 
followed  in  obtaining  the  formula.     From  a  comparison 
of  a  number  of  experiments,  the  value  of  K  gives 
c':^c[0.91  n4-U.09]3. 

736. ..The  preceding  method  is  also  applied  to  find  a 
formula  for  the  charges  of  undercharged  mines.  In  this 
case,  7?  and  ;•'  being  supposed  less  than  /•,  ''  ~~^-^^=K^  and 
hence  c''=:e[^-i''- "^]^-W- 

The  constant  K\\\  this  case,  is  determined  from  a  result 
of  experiment;  that  if  a  certain  charge  of  powder  forms  a 
common  crater  with  a  line  of  least  resistance  ^,  the  same 
charge  will  not  produce  any  external  effect  when  the  line 
of  least  resistance  is  increased  to  If  I  or  |  I ;  and,  recipro- 
cally, if  a  charge  produces  no  external  effect  with  a  line  of 
17 


258  MINES. 

least  resistance  I,  the  same  elinrfje  will  form  a  conmion 
mine  under  a  line  of  least  resistance  4  l-  Ifj  then,  the 
charge  c\  by  sup[)Osition,  does  not  produce  any  external 
eftect  under  the  line  of  least  resistance  I,  it  will  produce  a 
common  mine  under  a  line  of  least  resistance  ^  I ;  from 
this,  by  the  Miner's  Rule,  there  obtains 

c'  :c:\{^lf:l^, 
or,  c'=c{^Y. 

iSTow,  substituting  this  value  of  c'  in  Eq.  (X),  and  making 
?/=o,  its  corresponding  value  for  this  of  c' ;  there  obtains 
j,=  ,,  which  result,  substituted  in  the  same  Eq.  [X)  it  then 
becomes  c'^^c  [l — ^  (1 — n)]^;  hence  c'=c  {——Y-,  which  is 
the  formula  for  undercharged  mines. 

737... Gallery  Frames.  Temporary  galleries  are  made 
of  framework  covered  in  by  plank,  and  are  prepared  but 
a  short  period  before  they  are  required  for  use. 

738... The  frames  of  temporary  galleries  consist  of  four 
pieces :  two  uprights  termed  stanchions^  and  two  horizontal 
pieces,  the  one  at  top  termed  a  cap  sill,  and  the  bottom 
piece  a  ground  sill;  1*1.  8,  Fig.  A,  shows  the  connection 
between  the  parts  of  the  frame. 

The  plank  or  boards  which  cover  in  the  frames  are 
termed  sheeting.  The  top  sheeting  of  the  frames  usually 
consists  of  boards  from  3  feet  6  inches  to  4  feet  in  length, 
from  7  to  12  inches  in  width,  and  from  1  to  1|  inches 
thick.  The  side  sheeting  may  have  the  same  length  and 
breadth  but  need  not  be  thicker  than  from  |  to  1  inch. 
To  set  the  frames  up  and  retain  them  in  their  places,  slips 
of  plank  termed  battens  are  used,  which  are  about  2J  inches 
wide  and  1  inch  thick. 

The  frames  may  be  either  of  well  seasoned  oak  or  pine, 
the  latter  is  preferable  as  lightest.  The  parts  of  each  frame 
receive  the  dimensions  in  the  annexed  table: 

Great  gallery, ....  ground  sill   6"X4"^,  stanchions  6X6",  cap  all  7X6", 

Common  gallery,              "             5X4,  "  5X5,  "        6X5, 

Half  gallery,                     "           4|^X3i,  "        4^X4^,  "        5X4^, 

Branches,                           »           3i^X3,  "        3^X3^,  "      4^X3^, 

Small  branches,               "             3X3,  "  3X3,  "        4X3. 


MINES.  259 

739... Shaft  Frames.  PI.  8,  Figs.  3,  4,  5.  A  shaft  is  a 
vertical  pit,  lined  with  sheeting  on  the  outside  of  frames 
which  are  placed  horizontal!}',  and  at  suitahle  intervals 
apart. 

The  cross  sections  of  shafts  are  either  squares  or  rec- 
tangles; the  dimensions  of  the  sides  of  the  section  depend- 
ing on  the  ohject  of  the  shaft.  When  this  is  for  driving  a 
gallery  from  the  bottom  of  the  shaft,  the  dimensions  of  the 
shaft  frames,  in  the  clear,  must  be  at  least  equal  to  that  of 
the  gallery,  from  out  to  out  of  its  sheeting.  A  shaft,  sunk 
for  establishing  a  mine  chamber  simply,  should  usually  be 
of  the  least  dimensions,  which,  to  allow  the  miner  to  work 
with  facility,  must  not  be  less  than  3  feet  by  2  feet  in  the 
clear. 

Two  kinds  of  frames  are  usuallj^  requisite  in  sinking 
shafts:  a  top  frame,  Fig.  1,  formed  of  four  pieces,  halved  to 
tit  each  other,  which,  wdien  put  together,  have  the  same 
dimensions  in  the  clear  as  the  shaft,  each  piece  projecting 
beyond  the  side,  or  having  an  over  length  of  1|  to  2  feet; 
the  other  is  termed  a  side  frame,  Fig.  2,  and,  also,  consists 
of  four  pieces  of  smaller  scantling  than  the  top  frame, 
halved  at  the  ends  to  tit,  its  dimensions  in  the  clear  being 
the  same  as  the  other. 

In  very  loose  soil  it  may  be  necessary-  to  use  a  tempo- 
rary frame,  o,  Fig.  4,  termed  an  auxiliari/  frame.  This  is 
somewhat  larger  in  the  clear  than  the  })rece(ling.  Its 
uses  will  be  explained  farther  on. 

The  opposite  pieces  of  each  frame  are  marked  with  a 
saw  cut,  termed  a  score,  at  their  middle,  on  the  upper  side. 
The  scores  serve  to  fix  the  position  which  the  frame  should 
occupy  when  laid. 

The  scantling  for  top. frames  is  usualh^  6  inches  square  ; 
that  of  side  and  auxiliary  frames  4^  inches,  for  a  shaft  over 
4J  feet  in  the  clear.  For  smaller  shafts,  the  scantling  may 
be  of  smaller  dimensions. 

740...vShaft  Interval.  The  term  interval,  both  in  shafts 
and  galleries,  expresses  the  distance  between  two  adjacent 
frames  added  to  the  thickness  of  the  scantling  of  the  frame, 


260  MINES. 

measured  in  the  direction  of  tlie  axis  ot  the  shaft,  etc. 
With  scantling  and  sheeting  of  the  usual  dimensions, 
the  interval  should  not  be  greater  than  3|  feet. 

Pkob.,  Fig.  3.  The  depth  of  a  shaft,  and  the  height  of  a 
gallery  to  lead  from  the  bottom  of  the  shaft,  being  given,  to 
estimate  the  shaft  interval. 

Add  together  the  height  of  the  gallery  frame  from  the 
top  of  its  ground  sill,  the  thickness  of  the  top  sheeting, 
and  the  thickness  of  the  shaft  frame ;  to  this  sum  add  2 
inches  for  free  space  between  the  gallery  frame  and  the 
shaft  frame  next  above  it,  to  introduce  the  top  sheeting. 
Subtract  this  sum  from  the  depth  of  the  shaft,  and  divide 
the  remainder  into  any  convenient  number  of  equal  or 
unequal  intervals,  each  not  greater  than  3|  feet. 

Let  the  depth  of  the  shaft,  for  example,  be  22  feet,  and 
the  height  of  the  gallery  4'.G'''.     Then  : 

From  ground  sill  to  exterior  of  top  sill 4M1" 

Top  sheeting 0.1 

Shaft  frame 0.4i 

Free  space 0.2 

Total 5.61 

This  taken  from  22  feet  leaves  16'. 5|",  which  can  be 
divided  into  four  intervals  of  3'.4"  each,  leaving  one  inter- 
val of  3M|",  which  may  be  placed  either  at  top  or  bottom, 
but  best  in  the  latter  position. 

74I...C0NSTKUCTION  OF  Shaft.  To  construct  the  forego- 
ing shaft  in  a  loose  soil,  there  will  be  required  a  top  frame; 
five  side  frames  for  the  intervals  above  estimated ;  two  for 
the  remaining  lower  portion  of  the  shaft;  one  auxiliary 
frame ;  four  battens  for  each  interval  of  the  length  of  the 
interval  added  to  the  thickness  of  the  shaft  frame ;  from  12 
to  20  square  pickets  about  18"  long ;  with  the  machinery 
and  mining  tools  requisite  for  the  operation. 

742. ..The  work  is  laid  out  by  driving  a  picket  to  mark 
the  axis  of  the  shaft,  and  two  others,  which  with  the  first 
are  in  the  vertical  plane  containing  the  axis  of  the  gallery. 
A  level  bed  is  then  made  for  the  top  frame,  the  pieces  of 


261 

MINES.  '^"^ 


Which  are  accurately  hiid  and  conftnod  by  pickets  one  at 
the  end  of  each  piece;  cave  being  had  to  drive  the  t^^o 
pickets  of  each  piece  together,  so  that  its  trne  position  may 
;>e  kept.  Other  pickets  may  be  driven  temporarily  on  the 
outside  of  the  frame,  at  the  angular  points.  Aftei  the 
frame  is  laid,  the  accuracy  of  its  position  is  tested  by  seeing 
whether  the  distances  from  the  centre  of  the  centra  picket 
to  the  interior  angular  points,  or,  in  other  words,  the  -s.^.^- 
diacfonals,  are  equal ;  if  they  are,  the  position  is  correct. 

743     The    excavation    is  now   commenced,   and,   it   tnc 
crumbling  of  the  soil  does  not  interfere,  may  be  carried  as 
far  as  th^  position   of  the  iirst  side  frame;  the   sheeting 
boards,  inserted  between  the  soil  and  the  exterior  of  the 
ton  frame,  being  gradually  advanced  with  the  excavation; 
here  the  first  side  frame  is  hung  by  four  battens,  two  being 
nailed  to  each  piece  of  the  opposite  sides  of  the  top  frame 
aud  to  the  two  corresponding  pieces  of  the  side  frame,  the 
halvings  of  which  are  turned  upward;    after  these  pieces 
are  acljlisted  bv  their  scores  aud  fixed,  the  other  two  pieces 
nre  laid  on  them,  the  halvings  down,  and  secured  bynails 
744     This  frame  being  fixed,  the  ends  of  the  sheeting  ot 
the  next  interval  may  be  inserted  between  it  and  the  sheet, 
ino.   of  the   first   interval,  and  the   excavation   continued. 
The    soil    now   becoming   trcniblesoine   by  its    crumbling 
measures  must  be  taken  to  retain  it  firmly  until  the  second 
frame  is  laid.     For  this  purpose  the  auxiliary  frame  1  ig.  4, 
is  introduced,  and  hung  midway  in  the  interval,  like  the 
usual  frames.     The  sheeting  which  thus  far  has  been  gra.lu- 
ally  advanced  with  the  excavation,  is  also  inclined  outward 
at  bottom,  to  gain  room  fi>r  the  auxiliary  frame,  by  wedges 
inserted  between  the  boards  of  the  two  intervals    After  the 
auxiliarv  frame  is  fixed,  the  excavation   and  sheeting  arc 
carried  "on  to  the  l)ottom  of  the  interval,  the  next  frame 
Inino-    and   the  sheeting  for  the   new  interval  introduced. 
Thc^'auxiliary  frame  is  now  removed  and  placed  m  the  next 
position,  when  reached  by  the  excavation.     The  work  will 
proceed  in  this  order  until  the  shaft  is  completed;  when  so 
a  picket  is  driven  in  the  bottom.  Fig.  5,  to  mark  the  central 
point. 


262  MINES. 

Remark.  A  sketch,  made  to  a  suitable  scale,  should  be 
m  hand  for  immediate  reference  in  conducting  such  works. 
This  is  more  particularl}^  necessary  for  gallery  work,  the 
sketches  for  which  should  be  very  accurately  drawn,  refer- 
enced and  numbered,  as  they  serve  not  only  for  reference  to 
guide  the  miner,  but  to  determine  positions  and  dimensions 
of  some  of  the  important  portions. 

745... Combinations  of  Timber  Galleries.  A  gallery 
which  leads  from  another  is  termed  a  return,  and  is  called 
oblique  or  rectangular,  according  to  whether  the  projections 
of  the  axes  of  the  two  galleries  make  a  right  or  an  acute 
angle.  The  gallery  from  which  the  return  is  made  is 
termed  -ii  gallery  of  departure.  When  the  floor  of  the  return 
rises  or  falls  from  that  of  the  departure,  the  return  gallery 
is  termed  ascending  or  descending. 

746... Working  Plans.  To  make  a  working  sketch  of  a 
combination  of  galleries,  the  projections  of  the  axes  are 
first  laid  out ;  their  points  of  intersection  marked  ;  and  the 
distances  and  reference  between  all  the  points  written. 
The  half  width  of  each  gallery  in  the  clear  being  next  set 
off  on  each  side  of  its  axis,  a  line  is  drawn  for  it,  then  one 
parallel  and  exterior  to  it  at  the  thickness  of  the  gallery 
frame,  and,  finally,  a  second  to  mark  the  exterior  line  of 
the  shectino;. 

The  line  CD,  Figs.  6,  7,  8,  is  the  axis  of  the  gallery  of 
departure,  and  A  B  that  of  the  return.  The  line  a  h  \s,  the 
interior  line  of  the  gallery  frames;  c  c/ the  exterior  line  of 
the  same;  e/ that  of  the  sheeting.  The  oprresponding 
lines  for  the  remaining  half  of  the  gallery  of  departure,  and 
those  of  the  returu,  will  be  readily  recognized.  The  frames 
m  and  m'  bound  the  entrances  to  the  returns ;  and  those, 
M,  y,  of  the  auxiliary  return,  the  entrance  to  the  oblique 
return.  Fig.  8. 

The  case  of  a  change  of  direction  in  a  gallery  is  shown  in 
Fig.  9.  Here,  to  obtain  room  for  the  miner  to  handle  the 
sheeting,  etc.,  an  end  of  an  auxiliary  gallery  is  made  oft",  on 
the  salient  angle  of  the  break,  just  large  enough  for  the 
object  in  view.     Having  set  oft'  these  lines,  the  points  of 


MINES.  263 

intersection  of  the  exterior  lines  of  tlie  sheeting  of  tlie 
return  with  the  exterior  and  interior  lines  of  the  frame  of 
the  gallerj'  of  departure  are  marked  as  follows,  to  deter- 
mine the  distance  to  be  left  between  the  two  frames  of  the 
gallery  of  departure,  between  which  the  entrance  to  the 
return  is  placed:  1st,  when  the  projections  of  the  axes 
make  a  right  angle,  then  the  intersections  of  the  exterior 
lines  of  the  sheeting  with  the  interior  lines  of  the  frames 
are  marked;  the  entrance  to  the  return  will  be  equal  to  the 
distance  between  the  exterior  lines  of  the  sheeting  of  the 
return  ;  2d,  when  the  angle  is  between  45°  and  90°,  the 
intersection,  o,  of  the  exterior  line  of  the  sheeting  of  the 
return,  which  lies  within  the  angle  formed  by  the  axes, 
with  the  exterior  line,  c  (/,  of  the  gallery  frames,  and  that,  o', 
of  the  other  exterior  line  of  the  sheeting  with  the  interior 
line  of  the  same  frames  being  marked,  will  give  the  points 
between  which  the  frames  of  the  gallery  of  departure  must 
l)e  placed  to  form  the  entrance ;  3d,  when  the  angle  be- 
tween the  axes  is  less  than  45°,  the  frames  bounding  the 
entrance  to  the  return  would  fall  too  far  asunder.  It  will, 
therefore,  be  requisite  to  make  a  rectangular  auxiliary 
return  from  the  gallery  of  departure,  into  which  the  oblique 
return  w^ill  have  its  entrance.  To  determine  tlie  position 
of  the  rectangular  return.  Fig.  8,  a  line,  r  5,  is  iirst  drawn 
exterior  to  the  sheeting  of  the  gallery  of  departure,  and  at 
a  distance  from  it  equal  to  the  thickness  of  the  frames  to 
be  used  for  the  auxiliary  return  ;  the  intersection,  o,  of  the 
exterior  line  of  the  sheeting,  which  lies  within  the  angle  of 
the  axes  and  the  last  line  drawn,  being  marked,  will  give 
the  point  through  which  the  inner  line  of  the  frames  of  the 
auxiliary  return  is  to  be  drawn.  This  line  being  deter- 
mined, all  the  other  lines  for  this  return  can  be  readily  set 
out.  The  rest  of  the  problem  will  be  treated  as  in  the 
second  case. 

747. ..Remarks.  From  an  examination  of  the  above  cases, 
it  will  be  seen  that  the  object  to  be  accomplished  is  so  to 
jilace  the  two  frames  of  the  gallery  of  departure,  which 
bound  the  entrance  to  the  return,  that  the  stanchions  of 


264  MINES. 

these  frames  shall  not  be  in  the  way  of  the  miner  when 
l)ushing  forward  the  side  sheeting;  or,  in  other  words,  if 
the  return  were  a  box  that  could  be  pushed  forward,  like  a 
drawer,  in  the  direction  of  its  axis,  the  stanchions  in  ques- 
tion should  not  hinder  this  movement. 

Several  other  problems,  of  a  like  character,  may  present 
tliemselves  in  returns,  and  in  changes  of  direction  in  gal- 
leries, wdiicli  it  will  be  unnecessary  to  treat  here,  as  the 
illustrations  above  given  will  readily  suggest  the  methods 
to  be  adopted  for  their  solution. 

748. ..Determination  of  Gallery  Axes.  Having  set  oft" 
all  the  lines  on  the  working  sketch,  and  marked  the  posi- 
tions of  the  different  frames,  etc.,  at  the  junctions  of  the 
galleries,  their  forms,  dimensions,  and  also  their  exact  po- 
sitions with  respect  to  any  fixed  point,  can  be  accuratel}' 
determined  from  the  scale  of  the  sketch,  and  be  written 
upon  it  for  reference  in  conducting  the  work.  For  exam- 
ple:  in  Fig.  7,  the  determination  of  the  points  o  and  o',  fix 
the  positions  of  the  gallery  frames  m  and  m',  and  the  form, 
position  and  dimensions  of  the  oblique  frame  q,  of  the  re- 
turn, where  the  galleries  join.  Having  set  ofl:'  these  parts, 
the  point  /,  on  the  axis  of  the  gallery  of  departure,  equidis- 
tant from  the  points  k  and  z,  of  the  tVame  q,  can  be  deter- 
mined. This  point,  marked  by  a  picket,  serves  to  fix  these 
])oints,  and,  with  the  picket  at  F,  the  direction  of  vl  J5. 

749... Landings.  The  portion  of  the  floor  of  the  gallery 
between  the  frames  that  bound  the  entrance  to  a  return,  is 
termed  a  landing;  as,  for  example,  the  spaces  between  the 
frames  m,  m.\  and  m,  v.  The  landing  is  in  all  cases  horizon- 
tal, as  well  as  that  portion  of  an  oblique  return  between 
the  oblique  frame  q,  and  the  one,  x,  next  succeeding,  which 
last  should  not  be  placed  farther  than  an  ordinary'  interval 
from  the  farthest  point  of  q. 

750... Gallery  Intervals.  Having  determined,  by  means 
of  the  working  sketch,  tlie  landings  and  their  frames  with 
respect  to  the  points  of  intersection  of  the  axis  of  the  gal- 
lery of  departure  with  those  of  the  returns,  the  intervals  of 
this  gallery  can  be  calculated,  and  their  positions  marked 


MINES. 


265 


out  oil  the  sketch.     The  manner  of  making  this  estimate 
will  he  hest  illustrated  hy  the  following  example : 

Let  A  B  =  11S  feet,  Fig.  10,  he  the  total  length  of  a  gal- 
lery of  departure,  estimated  horizontall}'  along  its  axis, 
from  the  central  picket  of  the  shaft  from  which  tlie  gallery 
starts.  At  the  point  C,  44  feet  from  A,  the  axis  of  a  rec- 
tangular return  commences,  and  at  D,  44  feet  farther,  that 
of  an  ohlicpie  one.  The  part  A  C  of  the  gallery.  Fig.  11, 
is  to  he  a  common  great  gallery ;  the  part  C  D,  Fig.  12,  a 
common  gallery  ;  and  the  part  Di?,  Fig.  13,  a  great  hranch. 
With  these  data,  it  is  required  to  determine  the  intervals 
for  the  different  portions  of  the  gallery. 

To  find  the  interval  for  the  first  portion,  A  C,  suhtract 
from  the  total  distance,  44  feet,  the  following  aggregate : 

Half  the  width  of  the  shaft  in  the  clear 2'.2" 

The  thickness  of  the  lowest  shaft  frame 0.4i 

Half  the  width  of  the  landing  at  C 2.0| 

The  thickness  of  a  gallery  frame  at  the  landing 0.  5 

5'.0" 
which  leaves  39  feet  to  be  divided  into  suitable  intervals, 
which  may  be  done  by  making  twelve  of  them  each  3  feet 
3  inches. 

The  intervals  of  the  portion  CD,  will  be  found  as  fol- 
lows: from  44  feet  take  the  following  sum  : 

Half  the  width  of  the  landing  at  (' 2'.0i" 

Thickness  of  the   landing  frame 0.5 

The  distance  from  JD  (as  found  from  sketch)  to  the 

landing  frame  beyond 0.9 

Thickness  of  gallery  fi-ame  at  landing  D 0.4|^ 

3'T7^ 
which  leaves  40  feet  5  inches.  This  can  be  divided  into 
nine  intervals,  each  3'.1",  and  four  of  3'.2"  each. 

To  find  the  intervals  for  the  part  D  B,  from  30  feet  take 
the  following  aggregate  :* 

Distance  from  D  to  frame  of  landing  beyond  it 4'. 5" 

Thickness  of  landing  frame  beyond  D 0.3^ 

Thickness  of  last  frame  at  i? 0.3^ 


o' 


.0 


// 


266  MINES. 

This  leaves  25  feet,  which  can  be  divided  inti)  six  intervals 
of  3'. 2"  each,  and  two  of  3'. 

751. ..Slope-Block.  In  setting  the  ground  sills  of  fi-anies 
in  ascending  or  descending  galleries,  a  small  cubical  Idock 
of  wood,  termed  a  slope-block^  is  used.  This  is  a  cubical 
block,  the  edge  of  which  is  equal  to  the  difference  of  level 
between  the  ground  sills  of  an  interval.  To  determine  the 
height  of  the  slope-block  for  any  portion  of  a  gallery  where 
the  intervals  are  equal,  or  nearly  so,  the  diiference  of  level 
or  of  reference  of  the  two  extremities  of  the  portion  must 
be  divided  by  the  number  of  intervals.  Thus,  in  the  por- 
tion of  the  gallery  from  A  to  C,  Fig.  10,  there  is  an  ascent 
of  5',  or  60",  and  twelve  intervals ;  the  edge  of  the  slope- 
block  will,  therefore,  be  \l"=^^'.  In  the  portion  from  C 
to  D,  there  is  a  fall  of  4M,"  or  49",  and  thirteen  nearly 
equal  intervals;  the  edge  of  the  slope-block  will,  therefore, 
be  3". 7,  nearly. 

752... Auxiliary  Frames.  In  loose  soils,  besides  the 
ordinary  gallery  frames,  there  is  required,  as  for  shafts  in 
the  same  soils,  an  auxiliary  gallery  frame.  This  frame, 
Fig.  14,  0,  Fig.  15,  is  somewhat  wider  than  an  ordinary 
galler}'  frame,  and  somewhat  lower  than  it.  Its  cap  sill  is 
rounded  on  top,  and  has  two  mortices  on  its  lower  side,  to 
receive  the  tenons  with  which  the  two  stanchions  are  fin- 
ished. The  mortices  are  a  little  longer  than  the  tenons — 
the  latter  being  confined  in  them  by  wedges  when  the 
frame  is  set  up.  To  adjust  the  frame  when  set  up,  a  pair 
of  folding  wedges  are  placed  under  each  end  of  its  ground 
sill.  By  these  various  contrivances,  the  frame  can  be 
readily  set  up  or  taken  apart. 

753... Construction  of  Galleries.  To  explain,  now,  the 
practical  operations  in  driving  a  gallery,  let  an  example  be 
taken  where  the  soil  is  loose,  and  the  floor  of  the  gallery 
rises  from  the  point  of  departure.  In  this  case,  the  first 
frame  of  the  gallery  o,  Fig.  16,  must  be  set  up  within  the 
shaft  and  against  the  shaft  frames,  on  the  side  from  which 
the  gallery  is  to  open.  The  ground  sill  of  this  frame  being 
laid,  the  stanchions  are  secured  to  the  intermediate  shaft 


MINES.  2(J7 

frames  of  the  last  interval  by  battens,  and  the  top  sill  fast- 
ened. A  horizontal  beam,  c,  is  then  secured  to  the  under 
side  of  the  top  shaft  frame  of  the  same  interval,  to  pre- 
serve the  proper  slope  for  the  top  sheeting  when  inserted, 
wedges  being  placed  between  this  beam  and  the  sheeting 
board  for  this  object.  A  like  arrangement  for  the  side 
sheeting  may  be  made  if  necessary.  The  excavation  of 
the  gallery  is  now  commenced  at  top,  l)y  forcing  down  with 
a  crowbar  the  sheeting  of  the  shaft,  on  the  side  of  the  gal- 
lerj'.  The  earth  is  removed  graduall}'  forward  and  down- 
ward, and  the  gallery  she.eting  advanced  at  the  same  rate. 
When  the  excavation  has  reached  as  low  as  the  interme- 
diate shaft  frame,  the  piece  of  it  that  sustains  the  lower 
portion  of  the  sheeting  is  removed,  to  allow  the  excavation 
to  proceed.  When,  in  this  way,  the  earth  is  removed  as 
far  as  the  middle  of  the  first  interval,  the  auxiliary  gallery 
frame.  Fig.  15,  is  set  np,  to  support  the  top  and  side  sheet- 
ing until  the  second  gallery  frame  is  placed.  To  place  this 
last  frame,  the  position  of  the  ground  sill  is  first  deter- 
mined, Fig.  17,  l)y  placing  the  slope-block,  o,  on  the  ground 
sill  first  laid,  and  then,  by  a  common  mason's  level,  A, 
upon  the  side  of  which  the  interval  is  marked,  laid  upon 
the  slope-block,  bringing  the  top  of  the  ground  sill  on  the 
same  level  as  that  of  the  slope-block.  The  sill  being  ad- 
justed and  firmly  secured,  the  stanchions  are  next  set  up, 
and  secured  by  battens  to  the  stanchions  of  the  first  frame, 
and  the  cap  sill  is  secured  in  the  last  place.  The  adjust- 
ments of  the  stanchions  and  cap  sills  are  made  l)y  an  ordi- 
nary })lund)-line,  l:)y  means  of  which  the  edges  of  the 
stanchions  are  placed  vertically,  and  the  scores  on  the  cap 
and  ground  sills  brought  into  the  vertical  plane  of  the  axis 
of  the  galler}'. 

The  battens  are  placed  horizontally.  In  a  level  gallery 
they  are  nailed,  alternately,  at  4  and  8  inches  below  the 
cap  sill.  In  others.  Fig.  17,  they  are  nailed  4  inches  below 
the  lower  of  the  cap  sills  of  the  two  frames  which  they 
unite ;  this  will  bring  them  at  4  inches,  added  to  the  height 
of  the  slope-block,  below  the  other. 


268  MINES. 

The  auxiliary  frame  is  not  taken  down  until  wedges 
have  heen  placed  between  the  sheeting  and  the  frame  last 
placed,  in  order  to  introduce  the  boards  for  the  next  inter- 
val ;  and  these  last  are  kept  in  the  proper  direction,  as  the 
excavation  is  advanced,  by  wedges  inserted  between  them 
and  the  sheetino;  of  the  interval  finished. 

754... Branch  Galleries  a  la  Holland aise.  These  gal- 
leries are  of  the  same  dimensions  as  small  branches  ;  the 
frames  are  made  of  plank;  they  are  placed  touching  each 
•other,  and  serv^e  at  the  same  time  both  as  frames  and 
sheeting. 

Each  frame  consists  of  four  pieces;  the  stanchions  have 
a  tenon  at  each  end,  Fig.  18,  fitting  into  notches  cut  in  the 
cap  sill  and  ground  sill  to  receive  them. 

When  the  gallery  is  an  ascending  or  descending  one,  the 
ends  of  the  stanchions  are  cut  obliquely,  in  order  that  their 
sides  may  always  be  vertical. 

Fig.  19  is  a  plan  and  section  of  this  description  of  gal- 
lery. 

755... For  the  purpose  of  limiting  the  effect  of  explosion 
of  mines  upon  the  branches  leading  to  them,  and,  at  the 
same  time,  to  enable  the  miner,  acting  on  the  defence,  to 
push  forward  and  open  a  new  branch  toward  the  crater, 
a  portion  of  a  branch  leading  toward  the  mine  is  made  of 
heavy  frames  of  the  foregoing  construction.  The  timber 
recommended  for  the  pur})ose  is  oak,  and  the  pieces  of 
each  frame  are  12"  wide  and  4"  thick.  The  portion  of  this 
strong  framework,  at  the  extremity,  is  solidly  filled  in  with 
pieces  of  4"  scantling,  from  6  to  10  feet  in  length.  For 
a  branch  28"  high  and  24"  wide,  seven  horizontal  layers 
will  be  required,  each  layer  consisting  of  5  pieces.  The 
centre  piece  of  each  layer  may  have  a  rope  handle  at  its 
end  to  allow  of  its  being  drawn  out  readily.  Filled  in  this 
way,  and  having  earth  well  packed  between  the  pieces, 
branches  of  this  description  will  not  be  damaged  by  the 
explosion  of  mines  of  from  6  to  10  feet  line  of  least  resist- 
ance, even  when  the  mines  are  within  4 J  to  6  feet  of  the 
branch.  From  their  chief  object,  these  branches  are  termed 
by  the  French  rameaux  de  combat. 


MINES.  269 

756... Shafts  a  la  Boule.  These  shafts  are  lined  with 
frames  made  of  plank,  connected  together  as  shown  in 
Fig.  20. 

In  Fig.  21,  a  section  of  a  shaft  a  la  Boule  is  shown,  which 
is  sufRcientl}'  explanatory  to  render  any  other  description 
unnecessar}'. 

This  kind  of  shaft  can  only  he  nsed  with  advantage  in 
favorable  soil,  on  account  of  the  difficulty  of  introducing 
the  frames  sufficientl}'  near  each  other;  they  are  commonly 
placed  one  foot  apart,  as  shown  in  tlie  figure.  Large 
gabions,  6  feet  long,  and  from  3  feet  6  inches  to  4  feet  in 
diameter,  are  sometimes  used  for  lining  shafts  near  the 
surface,  smaller  gabions  being  introduced  as  the  work  is 
proceeded  with. 

757. ..For  the  purposes  of  quickl}'  establishing  small 
camouflets  and  fougasses,  a  boring  apparatus  has  been 
resorted  to,  the  diameter  of  the  boring  tool  being  4".  This 
machine  is  worked  like  ordinary  tools  of  this  kind.  It  is 
charged  for  explosion  by  inserting  powder  in  cylindrical 
cartridges  of  somewhat  less  diameter  than  the  shaft,  which 
are  well  rammed  forward;  or,  if  a  large  ciiarge  is  requisite, 
the  end  of  the  shaft  can  be  enlarged  by  a  tool  with  a  joint, 
which  will  admit  the  tool  to  be  so  adjusted  as  gradually  to 
increase  the  excavation  at  the  end.  Excavations  made  in 
this  \\'ay  are  termed  artesian  shafts  or  branches. 

758... Construction  of  Permanent  Galleries.  When 
the  floor  of  the  gallery  is  not  more  than  10  or  12  feet  below 
the  surface,  it  will  be  generally  best  to  oi)en  a  trench  for  the 
work.  The  Avidth  of  the  trench  at  the  bottom  should  be 
the  same  as  the  galler}^  from  out  to  out.  If  the  soil  is  very 
firm,  the  sides  of  the  excavation  may  be  made  nearly  per- 
pendicular; at  6  feet  above  the  bottom  of  the  trench  a 
berm  3  feet  wide  should  be  left,  and  at  6  feet  above  this 
another,  and  so  on  for  every  additional  depth  of  6  feet. 
These  berms  serve  the  place  of  scatfoldiugs,  to  pitch  the 
earth  out. 

If  the  soil  is  very  loose,  the  slopes  will  require  to  be 
sustained  by  a  sheeting  to  prevent  the  earth  from  caving 


270  MINES. 

ill.  After  the  masonry  is  completed,  the  excavated  earth 
is  carefully  replaced. 

759... When  the  construction  is  made  entirel}"  under 
ground,  a  wooden  galleiy  is  first  formed,  the  width  of 
which,  hetween  the  frames,  in  the  clear,  Fig.  22,  is  equal 
to  the  width  between  the  piers  of  the  permanent  gallery 
from  out  to  out;  its  height  being  such  that  there  will  be 
6  inches  between  the  crown  of  the  arch  on  the  exterior  and 
the  cap  sills.  The  top  and  side  sheeting  should  lap  about 
8  inches. 

When  the  galleiy  is  completed,  a  new  set  of  ground  sills 
are  laid  alongside  of  those  of  the  gallery,  their  length  being 
equal  to  the  width  of  the  permanent  gallery  in  the  clear, 
Fig.  23.  A  new  set  of  stanchions,  o,  o,  are  set  up  on 
these  sills,  to  support  a  new  set  of  cap  sills  of  the  same 
length  as  those  of  the  gallery.  Vertical  boards,  «,  are 
placed  alongside  of  stanchions  of  the  wooden  gallery,  and 
are  buttressed  against  the  sheeting  b\^  two  horizontal  pieces 
of  scantling,  c,  c,  one  near  the  top,  the  other  near  the 
bottom  of  the  gallery.  When  this  new^  arrangement  is 
completed,  the  frames  of  the  gallery  first  set  up  can  be 
taken  down  and  the  mason ly  commenced. 

The  foundations  of  the  piers.  Fig.  24,  are  laid  with  an 
interior  oft'set  of  6  inches.  The  piers  are  then  carried  up, 
the  lower  horizontal  buttress  being  gradually  shifted  up 
so  as  not  to  interfere  with  the  work,  and  the  lower  courses 
of  the  side  sheeting,  which  have  now^  become  unnecessary, 
being  removed.  When  the  piers  are  completed,  the  stan- 
chions are  taken  down  and  replaced  by  props,  p,  p,  resting 
on  the  outside  of  the  tops  of  the  piers. 

When  this  change  has  been  made,  the  way  is  clear  for 
turning  the  arch.  For  this,  four  common  centres,  A,  A, 
Figs.  25,  26,  made  of  boards,  will  be  requisite.  Each  of 
these  centres  is  18  inches  broad,  and  is  secured  to  a  rec- 
tangular frame,  o,  of  small  scantling  of  the  same  breadth, 
and  as  long  as  the  span  of  the  arch.  Each  centre  thus 
pre})ared  rests  upon  a  trestle,  q,  q,  of  sutficient  height 
to  bring  the  centre  in  its  true  position  to  receive  the 
masonry. 


MINES. 


271 


The  masons,  to  expedite  the  work,  commence  at  the 
middle  point  of  the  gallery,  where  two  of  these  centres 
are  placed  together,  and  close  the  arch  over  them;  the 
other  two  centres  are  then  placed  alongside  of  these,  and 
the  arch  in  like  manner  is  closed  over  them;  the  two  first 
are  then  taken  down,  and  removed  to  tlie  outside  of  the 
two  last  set  np,  and  the  arch  is  thus  carried  on  toward  the 
two  ends.  The  Avood-work  of  the  gallery  is  taken  down 
as  fast  as  the  masonry  supplies  its  place. 

760... In  the  main  galleries  of  communication,  arched 
recesses  are  formed  to  serve  as  depots,  etc.,  for  tlie  imple- 
ments of  the  miners.  These  recesses  are  from  (3  to  12  feet 
in  depth  and  usually  of  the  same  width,  and  may  be  placed 
at  intervals  of  15  or  20  feet  from  each  other.  Similar  dis- 
positions are  made  in  the  listening  galleries  for  the  maga- 
zines of  earth  required  for  tamping  the  mines;  small 
portions  of  galleries,  from  6  to  12  feet  in  length,  are  run 
out  at  right  angles  to  the  listening  gallery  for  this  purpose. 
A  sufficient  number  of  openings  must  also  be  left  in  the 
piers  of  the  listening  galleries,  for  the  construction  of  the 
branches  leading  to  the  mine  chambers. 

7Gl...In  loose  soils,  and  to  give  greater  resistance  to 
masonry  galleries  to  globes  of  compression,  it  has  been 
])roposed  to  give  them  a  cross  section,  of  an  oval  form, 
instead  of  the  one  above  given.  Galleries  of  this  form 
wouM  be  of  more  difficult  construction  and  cost  more  than 
•those  of  the  usual  form. 

762...AVhen  several  galleries  branch  ofl:  from  the  same 

point,  a  large  arched  chamber 
of  a  square,  or  any  polygonal 
form,  is  constructed,  which 
serves  for  a  depot,  and  is 
also  arranged  with  a  crenated 
wall  within  it  to  defend  the 
most  advanced  galleries.  In 
the  annexed  figure,  for  exam- 
ple, if  the  galleries  a,  a,  a,  «, 
meet  at  a  point,   the  square 


272  '  MINES. 

arclied  chamber,  h  c,  is  placed  to  connect  them,  and  within 
this  a  space,  B,  is  enclosed  b}-  a  thin  wall,  constructed  with 
loop-holes  to  lire  in  the  direction  of  the  most  advanced 
galleries,  a,  a,  d. 

763. ..The  piers  of  the  galleries  are  also  arranged  either 
Avith  grooves  or  oft'sets,  so  that  barriers  may  be  made 
within  them  for  defence  against  the  enemy's  miner  when 
he  penetrates  into  the  galler3^  In  some  cases  a  simple  pit 
is  dug  across  the  gallery  and  covered  by  boards,  which  are 
taken  up  when  the  communication  is  required  to  be  cut  off. 

7G4...MiNE  Chambers.  The  chamber  of  a  mine  is  a 
cavity,  A,  formed  to  receive  the  charge  of  powder,  Fig.  27. 

When  the  chamber  is  made  at  the  end  of  a  galler}^  the 
centre  of  the  chamber  is  placed  on  a  level  with  the  Hoor  of 
the  gallery.  It  is  usually  better  to  place  the  chamber  at 
the  end  of  a  small  branch  return  on  one  side.  When  the 
charge  is  not  to  be  exploded  immediately,  or  the  ground  is 
much  saturated  with  moisture,  it  should  be  placed  in  a  well 
pitched  wooden  case,  or  a  good  cask,  or  in  a  wooden  case 
covered  with  tarpaulin,  or  any  like  expedient  adopted  that 
may  be  at  hand — the  best  receptacle  is  a  water-tight  tin  case. 

In  dr}'  ground,  and  when  the  charge  is  to  be  soon  ex- 
ploded, canvass  bags  will  answer. 

If  the  case  to  contain  the  powder  is  not  mcn-e  than  2  feet 
square,  it  may  be  introduced  into  the  chamber  ready  made; 
if  of  a  greater  dimension,  it  must  be  put  together  in  the 
chamber,  the  pieces  to  form  the  sides  being  arranged  like 
the  frames  of  branches  a  la  Hollandaise. 

An  opening  is  left  at  the  edge  of  the  cover,  about  4 
inches  square,  for  the  introduction  of  the  charge,  and  a 
similar  one  in  the  side  to  receive  the  hose-trough. 

The  edge  of  a  cubical  case  to  contain  a  given  charge 
is  calculated  on  the  supposition  that  58.5626  pounds  of 
powder  are  equal  in  bulk  to  a  cubic  foot ;  and  1,000  cubic 
inches  will,  therefore,  contain  33.89  pounds.  From  this,  if 
P  represents  the  given  number  of  pounds  of  powder,  and 
^the  side  of  the  cubic  sought  in  inches,  then 
33.89  :  (10)3  ::P:  x\ 
X=3.09^P: 


MINES.  273 

That  is,  to  obtain  the  edge  of  the  cubical  case  in  inches, 
extract  the  cube  root  of  the  given  number  of  pounds  of 
powder  and  multiply  it  by  3.09,  or  3,>jj,  nearly. 

From  the  bursting  of  guns,  where  the  wad  has  not  been 
pressed  down  on  the  powder,  it  lias  been  thought  that  in 
charging  mines  a  like  increase  of  effect  would  be  produced, 
by  leaving  a  certain  free  space  around  the  case.  Experi- 
ments on  this  point  have  not  been  sufficiently  decisive  to 
lead  to  the  adoption  of  this  in  practice. 

765... Hose  Tuougiis.  The  hose  trough  is  a  small  wooden 
channel,  in  which  is  placed  a  linen  bag  filled  with  powder, 
and  termed  the  powder-hose,  to  fire  the  charge. 

The  bag  should  be  of  close  texture  and  well  sewed. 

These  troughs  are  made  Ih  inch  square  in  the  clear.  The 
four  pieces  of  which  they  are  composed:  the  sill,  sides  and 
top,  or  cover,  are  from  J  to  |  inch  each  in  thickness. 

A  trough  should  penetrate  the  powder  case  about  4 
inches,  and  should  exactly  fit  the  opening  left  for  it. 

It  is  fastened  to  the  floor  of  the  branch  by  nails,  through 
the  sill,  which  enter  small  pickets  driven  to  receive  them. 
Sometimes  the  sides  of  the  trough  are  confined  by  pickets 
to  prevent  its  being  disturbed. 

The  difterent  lengths  of  the  trouo-h  should  be  cut  to  fit 
exactly.  Each  })ortion  of  the  trough  should  have  its  cover 
well  fitted  and  secured  with  one  peg  only,  in  order  that  it 
may  readily  be  removed  to  introduce  the  powder-hose. 

The  trough  is  said  to  make  an  elbow  when  it  changes  its 
direction.  The  pieces  forming  an  elbow  should  be  firmly 
yet  simply  connected;  Figs.  28,  29,  show  the  most  common 
forms  of  elbows. 

7G0.. .Proportioning  Trains.  When  several  mines  are 
to  be  fired  at  the  same  moment,  it  is  necessary  so  to  pro- 
portion their  trains  that,  starting  from  the  same  point,  the 
distances  in  time  from  that  point  to  the  charges  may  be  all 
equal.  The  following  cases  show  the  manner  of  obtaining 
this  result: 

For  two  charges,  Fig.  30,  place  a  trough  on  the  shortest 
18 


274  MINES. 

line  from  tlie  one  to  tlie  otlier,  mark  tlio  centre  of  it,  and 
let  the  principal  trough  join  it  in  that  point. 

Vov  three  charges,  Fig.  31,  connect,  as  above,  the  two 
-which  are  nearest.  Let  a  trough  from  tlie  middle  point 
of  this  to  the  third  charge,  bisect  the  whole  length  of 
trough  between  this  third  charge  and  either  of  the  others; 
then  let  the  principal  trough  be  joined  to  this  last  point. 

For  four  charges,  Fig.  32,  tirst  connect  them  two  and 
two,  then  join  the  central  points  and  proceed  as  al»ove. 

The  elbows  of  a  trough  impede  the  communication  of 
the  fire,  for  which  an  allowance  must  be  made  when  pi-o- 
portiouing  the  trains,  each  elbow  being  valued  at  3  inches; 
thus,  if  on  one  side  of  the  point  where  the  principal  trough 
connects  is  one  elbow  more  than  on  the  other,  the  principal 
trough  should  be  placed  3  inches  nearer  to  the  charge  on 
that  side,  which  is  done  b}'  placing  it  1|  inches  from  the 
central  point  toward  that  side.  Square  elbows  impede 
somewhat  more  than  oblique  ones. 

Experience  has  shown  that  two  powder-hoses  may  be 
placed  Avithin  18  inches  of  one  another  if  covered  with 
earth,  and  exploded  separately  without  interference. 

767...Tampin(}.  Mines  are  tamped  either  Avith  earth  and 
sods,  with  earth  and  wood,  or  with  sand-bags. 

To  tamp  a  branch  with  sods  and  earth,  the  miner  first 
fills  the  branch  Avith  sods  for  a  length  of  3  feet,  commenc- 
ing at  the  chamber.  The  sods  are  piled  in  regular  layers, 
the  precaution  being  taken  to  throw  loose  earth  over  eacli 
layer,  to  fill  the  voids  between  the  sods.  When  this  length 
is  finished,  the  miner  fills  in  for  an  additional  3  feet  with 
earth,  which  should  be  Avell  packed.  Another  length  of 
sods  is  laid  of  3  feet,  and  so  alternately  through  the  entire 
branch. 

To  tamp  Avith  Avood  and  earth,  a  stout  shield  of  thick 
boards  is  first  placed  across  the  branch  and  firmly  but- 
tressed against  the  chamber,  the  branch  is  then  filled  with 
well  packed  earth,  resting  against  the  shield  for  a  length  of 
3  feet;  billets  of  round  or  square  timber  are  then  packed 
across  the  branch  for  a  len<2;th,  likcAvise,  of  3  feet;  another 


MINES.  275 

length  of  earth  of  the  same  thickness  is  packed  in  against 
the  wood,  and  so  on  for  the  entire  length  to  be  tamped ; 
finally,  at  the  end  of  the  tamping  another  shield  is  set  up 
and  firmly  buttressed. 

Sand-bags,  for  tamping,  are  of  the  ordinary  dimensions. 
To  tamp  "with  them,  a  shield  is  first  placed  against  the 
chamber  and  well  buttressed.  The  branch  is  then  filled 
up  with  sand-bags  laid  in  regular  layers,  loose  earth  being 
thrown  over  each  layer  to  close  the  joints.  This  is  the 
best  kind  of  tamping,  as  it  can  be  removed  most  speedily 
after  the  explosion. 

The  length  of  tamping  is  regulated  by  the  line  of  least 
resistance  of  the  mine  ;  the  part  of  the  branch  tamped 
equal  to  twice  this  line.  This  length  must  be  measured  in 
a  right  line  from  the  chamber  to  the  point  of  the  branch 
where  the  tamiiins;  terminates,  and  not  alono-  the  windinir*^ 
or  elbows  of  the  branch. 

768... As  tamping  is  a  laborious  operation,  and  requires 
considerable  time  to  do  it  thoroughly,  it  has  been  proposed 
to  insert  a  trough  of  4"  or  5"  section,  in  the  branch  or 
shaft  leading  from  the  mine  chamber  to  the  main  gallery, 
or  branch,  and  then  to  tamp  in  the  usual  manner  around 
the  trough.  Prepared  in  this  way,  the  charge  made  into 
cylindrical  cartridges,  or  else  the  })owder  }>laccd  in  succes- 
sive portions  in  a  cylindrical  vessel,  attached  by  a  joint  at 
its  bottom  to  the  end  of  a  rod,  can  be  shoved  forward 
through  the  trough  and  be  thi'owii  into  the  chamber  in  a 
very  short  time,  and  the  mine  be  immediately  afterward 
exploded. 

769. ..Methods  for  Explodixo.  The  most  common  meth- 
ods of  firing  mines,  are  by  the  use  of  the  monk  and  the 
box-trap.     These  two  methods  require  a  powder-hose. 

The  monk  is  a  bit  of  agaric,  1|  inches  in  length.  The 
train  to  be  fired  by  it  is  arranged  as  follows: 

(Stretch  the  extremity  of  the  hose  upon  a  sheet  of  paper, 
and  sprinkle  some  dry,  tine  powder  on  it  ;  cover  this  ])ow- 
der  over  with  another  sheet  of  i)apcr,  secured  at  its  four 
corners  with  dry  earth  or  stones  ;  pass  the  in(»nk  throui;h  a 


27G  MINES. 

hole  iu  the  upper  sheet,  and  let  it  project  half  its  length 
above  it,  its  base  being  plunged  in  the  [)Ovvder  on  the  bot- 
tom sheet ;  set  tire  to  the  monk  at  to[)  with  another  piece 
of  agaric,  termed  an  informer,  of  the  same  dimensions  and 
form  as  the  first,  and  retire  quickly. 

The  box-trap,  Fig.  33,  is  a  box  18  inches  high  and  6 
inches  wide  in  the  clear.  The  bottom  consists  of  a  piece 
of  plank  18  by  10  inches,  and  its  cover  is  fixed  at  one  side 
only  with  a  w^ooden  pin,  about  which  it  can  be  turned. 

At  6  inches  from  the  to[)  of  the  box  a  horizontal  slit  is 
made  in  one  of  its  sides,  and  grooves  in  the  two  adjacent 
to  it,  to  receive  a  piece  of  board,  which  ought  to  slide 
freely  in  this  arrangement.  In  the  lower  part  of  the  box 
an  opening  is  left  on  the  side  opposite  the  one  cut  for  the 
slide,  to  admit  the  powder-hose. 

To  fire  the  train,  place  the  box  against  the  extremity  of 
the  tamping  and  secure  it  well ;  tie  a  string  to  the  slide, 
and  lead  it  along  the  stanchions  of  the  gallery  on  pegs 
(iriven  for  that  purpose;  put  the  end  of  the  hose  into  the 
box  through  the  hole  left  for  it,  a,nd  spread  on  the  top  of  it 
some  dry  fine  powder;  then  put  in  the  slide  and  close  with 
eartli,  or  rags  of  sand-bags,  all  communication  between  the 
lower  part  of  the  box  and  the  branch  ;  place  a  star-match 
of  six  or  eight  points,  well  lighted,  on  the  slide;  replace 
the  cover,  then  pull  the  string  and  the  star  will  fall  below 
and  fire  the  mine. 

The  two  methods  above  described  have  the  inconveni- 
ence of  requiring  a  powder-hose,  which,  from  its  own 
explosion,  poisons  the  galleries.  They  have  also,  and 
more  particularly  the  monk,  the  defect  of  not  producing 
the  explosion  always  at  the  instant  desired. 

To  avoid  these  inconveniences  a  galvanic  current  has 
of  late  been  applied  to  fire  mines,  and  with  complete 
.success.  This  method  has  been  found  particularly  ser- 
viceable in  firing  charges  under  water. 

A  small  rocket.  Fig.  34,  with  a  hemispherical  head  of 
wood,  has,  also,  been  tried  successfully.  To  use  it,  a 
wooden   trougli   with    a   smooth   interior  must  be  placed 


MINES.  277 

from  the  charge  to  tlie  point  where  the  rocket  h  to 
start;  tin  tubes  have  been  roconiniended,  hut  are  found 
not  to  answei'.  The  rocket  is  then  phiced  in  the  end  of 
the  trough,  t\]e  (luick-inatch  with  wliich  it  is  provided  is 
lighted,  and  tlie  rocket  starts  with  very  great  velocity, 
penetrates  the  charge  and  fires  it. 

When  the  rocket  has  to  pass  elbows,  or  when  it  is 
desired  to  fire  several  mines  at  the  same  moment,  a 
rocket  is  placed  at  each  turn  of  the  trough,  with  its 
quick-match  secured  round  a  nail ;  the  first  rocket  arriv- 
ing at  the  i)oint  where  the  other  is  placed  fires  it.  In 
order  the  better  to  insure  the  first  rocket  firing  the  second, 
a  quantity  of  })owder  (|  ounce)  should  be  strown  about  the 
match  of  the  latter,  [trotected  l)y  a  wedge-shaped  slip  of 
deal,  nailed  to  the  bottom  of  the  trough  ;  the  rocket  meet- 
ing this  passes  over  the  powder,  which  its  rapid  motion 
would  otherwise  disperse. 

A  rocket  maj'  be  made  to  turn  in  a  circular  trough, 
when  the  radius  of  that  part  is  not  less  than  twice  the 
length  of  the  rocket. 

Tn  order  to  j»revent  the  smoke  of  the  charge  penetrating 
the  gallery  through  the  trough,  one  or  two  small  iron  traps 
may  be  [ilaced  in  the  trougli,  which,  being  raised  by  the 
rocket,  fall  again  by  their  own  weight,  and  cut  otf  all  c-om- 
munication  between  the  gallery  and  the  charge. 

A  rocket  G  inches  long  will  travel  100  yards,  at  least, 
and  its  velocity  is  so  great  that  two  rockets  fired  at  the 
same  moment,  to  run  very  difi'erent  distances,  leave  no 
perceptible  interval  in  the  times  of  their  arrival.  This 
property  of  rockets  renders  it  eas}-  to  proportion  the  trains 
of  mines  to  be  fii'cd  Kiniultaneously,  which  with  powder- 
hose  requires  great  nicety. 

The  ordinary  rocket  for  this  service  contains  |  of  an 
ounce  of  a  composition  formed  |  of  fine  powder,  |  of  salt^ 
})etre,  and  |  of  charcoal  dust.  These  ingredients  should 
be  very  carefully  mixed,  to  make  the  rocket  burn  uni- 
formly. Its  usual  diameter  is  nearly  |  of  an  inch,  and 
entire  weight  about  1|  ounce.  Rockets  nniy  be  nnidc 
much  smaller  when  required. 


278  MINES. 

770... The  great  advantages  offered  by  galvanic  batteries 
for  exploding  mines  at  considerable  distances  from  the 
battery,  either  when  isolated  or  combined  in  groups  for 
simultaneous  effects,  have  led  to  experiments  which,  from 
the  uniform  certainty  of  the  results,  besides  other  obvious 
advantages  over  any  of  the  other  methods  above  given, 
will,  probably,  cause  the  general  adoption  of  this  apparatus 
for  militaiy  mines. 

The  method  mostly  adopted  by  the  Continental  engineers 
is  the  combination  of  Bunsen's  battery  with  Ruhmkorf's 
apparatus  for  intensifying  the  current  of  induction.  A 
copper  conducting  Mnre,  which  is  insulated  by  one  or  two 
coats  of  gutta-percha,  connects  the  charges  with  the  gal- 
vanic apparatus.  The  charge  is  exploded  by  passing  a 
spark  througli  a  ver^-  small  portion  of  fulminate  of  mer- 
cury inserted  between  the  ends  of  two  copper  wires,  which 
are  enclosed  within  a  short  tube  of  gutta-percha,  coated 
within  with  sulpliuret  of  copper.  The  w'ires  are  bent  near 
the  end  of  the  tube,  and  twisted  around  each  other.  A 
little  meal  powder  is  thrown  around  the  fulminate  and  the 
tube,  wdiich,  with  the  tube  and  the  bent  part  of  the  wire, 
is  tightly  closed  in  a  small  gutta-percha  bag,  to  keep  out 
moisture.  To  fire  a  single  mine,  one  end  of  the  twist  is 
soldered  to  the  conducting  wire  and  the  other  inserted  into 
the  earth  to  complete  the  circle.  For  several  mines,  to  be 
exploded  at  the  same  time,  conducting  wires  connect  the 
mines,  and  the  ends  of  the  twist  are  soldered  one  to  each 
conductor  except  the  end  one,  which  has  one  of  its  ends 
inserted  into  the  earth.  By  this  combination,  the  series 
will  be  exploded  without  any  sensible  difference  of  time 
between  the  nearest  and  furthest  mine. 

771... Blasts.  Blasts  are  small  chambers,  or  holes  made 
in  rock,  or  masonry,  charged  with  powder.  The  forming 
of  blast-holes  requires  the  use  of  particular  tools,  called 
borers,  jumpers,  scrapei^s,  needles  and  iamping-bars. 

To  form  the  blast-hole,  two  or  three  men  are  required  ; 
one  holds  the  borer  with  both  hands,  while  the  head  of  it 
is  struck  with  sledge-hammers  by  one  or  two  others.     The 


MINES,  279 

first  turns  the  borer  at  each  stroke  so  that  the  hole  may 
be  circular,  and  from  time  to  time  clears  it  out  with  the 
scraper. 

When  the  liole  required  does  not  exceed  15  inches  in 
depth,  it  may  be  excavated  in  the  above  manner;  but  if 
20  inches  or  more  deep,  the  jumper  is  generally  made  use 
of.  The  miner  holds  the  jumper  in  both  hands,  raises  it, 
and  lets  it  fall  in  the  hole,  turning  it  continually  ;  he  also 
clears  the  hole  with  the  scraper.  When  the  stone  is  of  a 
very  hard  description,  it  is  usual  to  pour  water  occasion- 
ally into  the  jumper  hole. 

To  load  the  hole,  fill  about  one-fourth  or  one-third  of  it 
with  powder,  according  to  the  nature  of  the  stone.  The 
charge  for  a  depth  of  18  inches  is  from  8  to  12  ounces. 

To  tamp  and  prime  the  blast-hole,  the  needle  is  first 
introduced,  plunging  it  well  into  the  powder  and  placing  it 
on  the  smoothest  side  of  the  hole  ;  then  a  layer  of  clay  is 
laid  on  the  powder,  and  is  closel}^  pressed  down  with  the 
taniping-bar. 

Other  similar  layers  are  then  laid,  or  layers  of  brick 
reduced  to  small  bits,  the  needle  being  turned  repeatedly. 
It  is  usual  to  press  down  the  first  layers  with  a  bar  of 
wood — the  helve  of  a  tool,  for  instance — and  the  latter  ones 
with  the  iron  tamping-bar.  When  the  hole  is  thus  filled 
up,  a  small  shell  of  clay  is  formed  round  the  needle,  which 
is  then  withdrawn,  the  hole  left  by  it  is  filled  with  fine 
powder,  and  it  is  fired  with  a  monk  or  a  piece  of  port-fire. 

The  use  of  the  needle  is  often  dispensed  with,  in  which 
case  the  priming  is  rolled  up  in  a  sheet  of  brown  paper,  or 
it  is  introduced  in  straw-stalks  thrust  into  one  another. 
This  priming  is  placed  in  the  hole  at  the  same  time  as  the 
charge,  so  that  it  may  penetrate  well  into  the  latter.  The 
tamping  is  then  executed  as  before. 

The  use  of  the  tamping-bar  and  the  ordimiry  taiuping 
may  also  be  dispensed  with,  the  hole  being  filled  over  the 
charge  with  very  fine  dry  sand,  poured  in  without  any 
[iressijre. 

The    many   accidents    that    have    ha|)pened    in    priming 


280  MINES. 

})lasts  have  led  to  the  invention  of  priming-fuses,  which  are 
made  to  burn  somewhat  in  the  same  way  as  the  fuse  in  the 
small  Chinese  fire-cracker.  Their  use  is  far  safer  than  any 
of  the  former  methods. 

For  blasts  under  Avater,  the  charge  is  inserted  in  a  water- 
tight tin  case,  and  fired  either  by  a  galvanic  current  or  a 
})riming-fuse,  which  is  protected  from  the  water  by  a  small 
tube  connected  with  the  charge,  and  leading  to  the  surface 
of  the  water. 

The  result  of  many  experiments  has  shown  that  in  blast- 
ing rock  a  large  portion  of  the  powder — nearly  half — may 
be  saved,  by  mixing  with  the  remaining  part  fine  dry  saw- 
dust of  elm  or  beech.  In  blasts  exploded  in  this  way,  the 
eftect  is  not  the  same  as  wlien  the  full  charge  of  powder  is 
used ;  the  rock  splits  into  fewer  and  larger  pieces,  and,  to 
finish  dividing  them,  a  more  frequent  use  of  the  sledge- 
hammer is  required. 

772... Demolitions.  The  charges  of  mines  intended  to 
overthrow  masonry,  are  calculated  as  in  a  conmion  soil,  by 
using  the  proper  quantities  given  in  the  preceding  table  for 
the  different  kinds  of  masonry  to  be  destroyed. 

773. ..To  Breach  a  Wall.  First  ascertain,  if  practicable, 
the  thickness  of  the  wall,  and  then  proceed  thus  : 

First  case.  \¥hcn  the  wall  is  from  2  to  3  feet  thick,  place 
one  or  two  barrels  of  powder  against  the  lower  part  of  it, 
and  fire  them. 

Second  case.  When  the  wall  is  from  5  to  6J  feet  thick, 
place  one  or  two  charges  under  its  foundations,  plumb  with 
the  centre  of  the  wall. 

Third  case.  When  the  wall  is  from  9  to  12  feet  thick, 
open  at  the  foot  of  it,  or  about  12"  above  the  water  level,  a 
branch  gallery,  which  must  be  driven  to  the  centre  of  the 
wall  ;  then  make  two  perpendicular  returns  to  this  branch, 
and  place  the  powder  at  their  extremities.  Fig.  35. 

774... To  Breacu  a  Wall  with  a  Tehhace.  Open  at  the 
foot  of  the  wall,  or  12"  above  the  level  of  the  water,  a 
branch  per[)endicular  to  the  direction  of  the  revetement; 
drive  it  through  the  wall  to  the  earth,  then  make,  to  the 


MINES,  281 

right  anrl  loft,  two  other  hraiiehes,  following  the  hack  of 
the  wall,  and  each  in  length  equal  to  its  thickness  ;  place 
the  charges  at  the  end  of  these  branches,  so  that  the  centre 
of  each  charge  may  be  flush  with  the  back  of  the  wall. 

775... Demolition  of  Revetements.  When  the  revotement 
is  without  counterforts,  or  the  counterforts  are  not  more 
than  3  feet  thick,  several  branches  are  driven  pci'}ien(licular 
to  the  direction  of  the  rcvetcnient,  at  equal  distances  apart. 
The  charges  used  should  produce  craters  that  will  cross 
each  other  a  little. 

When  the  wall  has  counterforts  of  the  usual  dimensions, 
the  charges  are  placed,  as  fiir  as  practicable,  in  the  lines  of 
their  axes  and  their  junction  with  tlie  revetement.  Fig.  36. 

When  time  presses,  instead  of  making  one  branch  for 
each  pair  of  charges  one  is  made  for  each  charge;  and  the 
whole  of  the  charges  are  placed  at  three-fourths  of  the 
thickness  of  the  wall,  a\id  so  regulated  that  their  craters 
may  slightl}'  run  into  each  other,  Fig.  37. 

When  galleries  cannot  be  driven  at  the  [)roper  level  for 
the  charge,  as  in  the  demolition  of  wharves,  etc.,  shafts  are 
sunk  behind  the  revetement,  or  at  a  short  distance  in  the 
rear  of  it.  Fig.  38,  and  branches  are  then  driven  to  the 
})ositions  for  the  charges;  or,  which  is  still  better,  because 
it  is  a  more  s[)eedy  o])ei'ati()n,  a  shaft  nuiy  be  sunk  for  each 
charge. 

The  depth  of  the  shait  must  be  sutHcient  to  admit  of  a 
})ro})er  length  of  tanqung. 

If,  at  the  same  time  with  the  wall,  a  mass  of  earth  in 
the  rear  of  it  is  to  be  destroyed,  prolong  the  branches  in 
the  interior  of  the  eaiih  sufficiently  to  allow  of  the  mines 
at  the  back  of  the  wall  exploding  before  those  placed  in 
the  earth  beyond.  Fig.  39. 

When  there  is  a  gallery.  Fig.  40,  at  the  back  of  the 
revetement,  the  charges  should  be  placed  along  this  gallery, 
excavating  chand)ers  for  them  in  tlie  revetement  at  dis- 
tances apart  equal  to  twice  their  line  of  least  resistance, 
viz.,  at    two  lined  intervals. 

The  ])orti()ns  of  the  gallery  in  the  rear  of  the   charges 


282  MINES. 

are  tlieii  tamped;  at  each  end,  the  length  of  the  tamping 
sliould  be  equal  to  twice  the  line  of  least  resistance  of  the 
extreme  charges. 

The  following  method  has  been  employed  with  success. 
Regarding  as  the  line  of  least  resistance  the  distance  from 
the  gallery  to  the  surface  of  the  wall,  imagine  a  row  of 
common  mines  placed  at  tw^o  lined  intervals  throughout 
the  length  and  calculate  the  sum  of  their  charges,  to  which 
add  one-half  for  a  great  gallery;  [)lace  the  whole  charge 
ill  several  heaps,  with  strong  trains  leading  from  one  to 
another.  Then,  tamp  strongly  and  carefully  the  ends  of 
the  gallery,  leaving  the  space  intended  to  be  demolished- 
void.  When  the  galler}-  is  more  than  2  yards  wide  and 
high,  or  if  it  have  many  issues  difficult  to  tamp,  the  charge 
of  powder  must  be  farther  augmented  to  produce  the 
desired  effect. 

776... Demolition  of  Towers.  If  the  interior  diameter 
of  the  tower  be  6  3'ards  or  more,  Fig.  41,  drive  branches 
into  a  wall  from  the  interior  of  the  tower,  and  place 
charges  so  as  to  be  a  little  nearer  to  the  interior  than 
to  the  exterior  of  the  Avail.  When  tlie  tower  is  connected 
with  walls,  charges  must  be  placed  at  their  points  of 
junction. 

When  the  tower  is  but  4  or  5  yards  in  diameter.  Fig.  42, 
sink  a  shaft  to  about  the  level  of  the  bottom  of  the  founda- 
tions, and  place  a  charge  there  corresponding  to  the  line  of 
least  resistance,  measured  from  the  centre  of  the  charge  to 
the  foot  of  the  Avail  outside. 

Cover  the  floor  of  the  toAver  with  two  roAvs  of  small 
beams,  then  lay  upon  them  two  beams  crossing  and  halved 
into  one  another;  and  place  upon  these  uprights  abutting 
firmly  against  the  masonry  of  the  arch. 

When  a  shaft  cannot  be  sunk  on  account  of  Avater, 
and  Avhen  the  tower  has  loop-holes  which  prevent  charges 
being  placed  in  the  walls,  lay  the  charge  on  the  floor  of  the 
tower,  enclosed  in  a  strongly  constructed  case,  propped  on 
all  sides  against  the  masonry. 

When   the   tower   is   square,  and  has   several    floors  or 


MINES.  283 

stages,  the  charges  may  be  placed  at  the  four  corners  of 
the  ground  story,  tamping  the  first  floor. 

777... Demolition  of  Powder  Magazines.  Phice  cliarges 
in  the  piers  and  gable  ends,  so  that  their  craters  may 
slightly  cross  each  other. 

When  time  presses,  a  charge  is  laid  on  the  floor  of  the 
magazine,  the  (h>ors  are  barricaded,  and  it  is  fired  with  a 
hose  led  outside. 

To  determine  the  quantity  of  powder  required  for  the 
heap,  calculate  the  number  of  common  mines  recpiired  to 
overturn  a  revetement  of  the  same  length  aiul  thickness  as 
the  walls  of  a  magazine,  including  the  piers ;  add  one-half 
the  sum  of  the  charges  thus  found,  and  place  the  whole  in 
one  heap  in  the  centre  of  the  magazine. 

The  above  method  is  only  applicable  to  magazines  of  not 
more  than  150  square  yards  surtace.  If  of  greater  capa- 
city, the  quantity  first  found  sliould  be  increased  j'g  for 
every  15  square  yards  of  additional  surface,  and  be  placed 
in  tw^o  or  more  heaps,  connected  with  powder-hose  to  fire 
them  simultaneously. 

778... Demolition  of  Bridges.  To  destroy  a  bridge,  the 
piers  of  which  are  from  4  to  5  feet  thick,  place  in  one  of 
the  piers  two  charges  of  130  to  160  pounds  each,  Fig.  43, 
and  secure  a  plaidc  to  the  bridge  on  which  to  place  the 
pow'der-hose. 

If  the  pier  l)e  from  6  to  10  feet  thick,  di'ive  in  the 
middle  of  it,  parallel  to  its  face,  two  small  branches,  at 
the  ends  of  which  [)lace  charges  of  from  200  to  230  jiounds 
each.  Fig.  44. 

When  there  is  not  time  to  place  charges  in  the  interior 
of  the  piers,  cut  a  trench  over  the  key  of  the  arch  18  inches 
deep,  in  which  place  400  to  530  pounds  of  powder. 

This  quantity  of  powder  has  broken  semicircular  arches 
of  26  feet  span,  and  4^  feet  thickness  at  the  crown. 

Another  good  method  is  to  cut  a  trench  in  the  form  of  a 
cross.  Fig.  44,  over  the  middle  of  the  arch,  each  branch 
being  about  10  feet  long,  and  carried  down  to  the  extrados. 


284  MINES. 

Place  in  each  branch  200  pounds  of  powder  for  an  arch  3^ 
feet  thick,  and  cover  tlie  charji^cs  with  timber,  earth,  etc. 

An  arch  may  also  be  l)lown  up  bv  suspending  an  open 
trough  under  it  with  cords,  and  placing  in  it  charges  of 
powder  similar  to  those  already  stated  for  trenches  cut  on 
the  surface. 

"When  the  saving  of  powder  is  of  consequence,  sink  a 
sliaft  down  to  one  of  the  haunclics,  Fig.  45,  and  place  tlic 
powder  in  one  mass,  unless  the  bridge  be  very  wide.  An 
arch  of  18  inches,  or  2  feet  thickness  of  a  bridge  20  feet 
wide,  may  thus  be  destroyed  with  45  pounds  of  powder,  if 
a  loading  can  be  applied  over  the  charge,  giving  an  equal 
resistance  to  the  arch. 

Tf  the  bridge  is  more  than  20  feet  wide,  two  shafts  must 
be  suidv,  and  charged  as  before  described.  When  the  side 
walls  of  the  bridge  above  the  piers  are  slightly  built,  and 
the  loading  of  the  arch  is  of  loose  rubbish,  a  small  gallery 
should  be  driven  about  5  or  6  feet  from  the  arch  stones, 
along  the  axis  of  the  pier,  as  at  A,  Fig.  45;  a  return  is 
then  made  toward  the  arch,  and  the  charge  is  placed  in 
contiict  with  the  extrados.  Bridges  of  timber  may  be 
blown  up  by  suspending  barrels  of  powder  under  one  or 
several  bays. 

779. ..Demolition  of  Houses.  Begin  by  undermining  the 
windows  and  doors,  and  cutting  away  the  piers  between 
them,  so  as  to  leave  the  building  supported  by  a  few  piers 
only,  nearly  square.  Place  in  each  of  the  piers  a  charge  of 
from  13  to  16  pounds  of  powder,  tamping  well  with  wood, 
Pro[K)rtion  the  trains  to  the  different  charges,  so  that  they 
may  be  simultaneously  exi)loded.  If  pressed  foi-  time, 
resort  to  the  same  methods  as  for  towers  and  galleries. 

To  destroy  palisades,  or  gates,  doors,  etc.,  the  best 
method  is  to  suspend  a  leathern  bag,  filled  with  powder, 
either  with  a  forked  stick,  a  strong  gindet,  or  a  stout  cop- 
per nail,  against  the  gate  or  palisade.  The  bag  should 
have  about  an  inch  of  port-fire  finnly  secured  in  one  side 
of  it,  to  communicate  the  fire  to  the  charge.     To  throw 


MINES.  '  285 

down  a  strong  palisade,  from  30  to  50  pounds  of  powder 
should  be  used.  To  burst  open  a  town  gate,  60  or  70 
pounds  of  powder  will  be  required; 

780...FOUGASSES.  Mines  are  so  ealled  when  placed  at 
the  bottom  of  small  shafts,  from  9  to  12  feet  deep.  The 
powder  is  lodged  in  one  of  the  sides  of  the  shaft,  and  it  is 
fired  from  a  secure  spot  by  means  of  a  powder  hose, 
brought  up  one  side  of  the  shaft,  and  carried  in  a  trough, 
parallel  to  the  ground,  5  or  6  feet  below  tli.e  surface.  When 
there  is  no  occasion  to  fear  that  shells  may  fall  on  the  part 
where  the  trough  is  laid,  it  will  be  sufficient  to  place  it  2 
or  21  feet  under  the  ground.  The  powder  case  and  trough 
should  be  well  pitched,  the  shaft  tami)cd  in  the  strongest 
manner,  and  the  earth  round  about  the  shaft  be  dug  over, 
that  nothing  may  indicate  to  the  enemy  the  positionof  the 
fougasse. 

781. ..Shell  Fougasses.  Shells  may  be  buried  singly,  or 
in  small  heaps,  and  be  made  to  burst  either  under*^  the 
ground  or  on  its  surface. 

^  If  they  are  to  burst  under  the  earth,  they  must  be  suf- 
ficiently charged  to  produce  a  crater,  through  which  the 
pieces  are  projected. 

If  they  are  to  burst  on  the  surface,  the  requisite  quantity 
of  powder  to  produce  a  crater  and  throw  out  the  shells 
must  be  lodged  under  them,  while  these  latter  need  only 
have  a  sufficient  charge  tc;  burst  them. 

In  all  cases  a  box  is  used,  Fig.  46,  divided  into  two  parts 
by  a  partition.  The  shells  are  placed  in  the  upper  part, 
their  fuses  project  through  the  partition,  and  extend  from 
^  to  1  inch  below  it. 

In  the  lower  part,  the  hose  only  is  phiced  wlien  the  shells 
are  intended  to  produce  their  own  crater;  but  powder  suf- 
ficient to  produce  the  crater  is  introduced  when  they  are 
intended  to  burst  on  the  surface  of  the  ground. 

The  effects  produced  by  common  and  shell  fougasses  are 
very  limited,  and  only  destructive  near  to  their  craters: 
consequently,  they  should  not  be  exploded  until  the  enemy 
is  above  them. 


286 


MIXES. 


DKScnirTiON 

OF  Shell. 

F 

ULL  Charge  of 

Shell. 

THE 

Depth  at  which  the  fuli^ 
chaugf.  produces  a 

Crater. 

Lbs. 

Oz. 

Calibre, 

H 

1 

0 

2' 

0" 

« 

8 

2 

9 

2 

10 

11 

10 

5 

0 

3 

6 

11 

13 

^ 

11 

0 

4 

7 

782... Conditions  to  be  satisfied  in  arranging  a  System 
OF  Mines.  As  the  galleries  of  a,  system  of  mines  serve  the 
purpose  of  uiKlergi'OUiul  communications,  they  should  be 
sulijected  to  the  same  conditions  as  other  communications. 
A  condition  of  primary  importance  is,  that  no  combination 
shall  be  made  which  might  compromise  the  safety  of  the 
enceinte.  To  this  end,  no  gallery  under  the  glacis  should 
lead  to  the  interior  of  the  enceinte  ;  for,  should  the  enemy 
get  possession  of  such  a  gallery,  he  might  either  penetrate 
into  the  work  or  else  barricade  the  galleiy  and  hold  pos- 
session of  it  long  enough  to  blow  up  the  works  under 
which  it  leads. 

783... The  galleries  should  not  offer  any  facilities  to  the 
besiegers  for  carrying  on  their  works.  Those  galleries, 
therefore,  which,  debouching  in  the  ditclies,  might  serve 
the  besiegers  for  their  descent  of  the  ditch ;  also,  a  con- 
tinued counterscarp  gallery,  which  may  not  only  facilitate 
the  descent  of  the  ditch  of  the  besiegers,  but,  also,  when  in 
their  possession,  give  them  that  of  the  whole  system,  and, 
besides,  serve  to  protect  their  passage  of  the  ditch,  and  to 
prevent  sorties  in  it,  should  be  rejected.  A  gallery  behind 
a  portion  of  the  counterscarp  not  favorable  to  the  enemy's 
works,  is  very  useful  as  a  depot  for  the  implements  of  the 
miners,  and  also  as  a  communication. 

784... A  permanent  system  of  mines  should  not  be  used, 
either  for  works  that  can  l)e  carried  by  storm  or  for  cov- 
ered-ways in  a  similar  state;  for  the  reason  that  the  besieg- 


MINES.  287 

ers  might  easily  get  possession  of  tlie  system  before  it  could 
he  brought  into  play. 

785...T]ie  dtbouche  of  a  system  in  the  ditches  must  be 
revetted,  to  offer  a  suflicient  obstacle  to  prevent  the  enemy 
from  getting  possession  of  the  system  by  surprise ;  hence, 
a  revetted  counterscarp  is  a  necessary  condition  in  the 
establishment  of  the  system. 

786. ..The  galleries  should  not  be  run  out  to  any  consid- 
erable distance  l)eyond  the  covered-ways,  both  on  account 
of  procuring  a  good  circulation  of  air,  and  because  very 
advanced  galleries  are  easily  destroyed  by  the  besiegers. 
The  distance  to  wliich  the  galleries  may  extend  should  be 
so  much  the  less,  as  the  ground  above  them  is  well  pro- 
tected by  the  collateral  works. 

787...Tlie  soil  must  be  suitable  for  the  establishment  of 
a  system  ;  wet,  marshy  ground,  shifting  sand,  and  hard 
rock,  present  almost  insuperable  obstacles ;  whereas,  a  dry, 
tirm  soil,  soft  rock,  or  ordinary  earth  under  a  thin  super- 
stratum of  hard  rock,  are  very  favorable  circumstances.  If 
the  sub-soil  is  wet,  but  presents  a  firm  and  dry  superstra- 
tum 12  feet  thick  above  the  level  at  which  the  water  col- 
lects, mines  may  still  be  placed  with  advantage. 

788... Besides  the  above  general  conditions,  there  are 
certain  special  ones  to  be  attended  to  in  arranging  the 
galleries  and  chambers. 

The  galleries  should  be  placed  as  far  below  the  surface 
as  pi-acticable,  to  withdraw  them  from  the  effect  of  the 
globes  of  compression  of  the  besiegers.  To  drain  the 
galleries  the}'  sliould  have  a  sliglit  inclination,  about  ^'g, 
toward  the  ditclies,  or,  if  the  ground  descends  toward  a 
hollow,  the  inclination  may  be  given  in  that  direction. 

789... The  clnuubcrs,  on  the  contrary,  should  be  near  the 
surface ;  by  this  arrangement  the  powder  is  economized, 
and  all  danger  to  the  galleries  from  the  explosion  avoided, 
whilst  the  object  of  the  mines,  which  is  to  destroy  the 
enemy's  works,  can  be  as  fidly  attained  by  small  mines  as 
large  ones. 

700. ..The  galleries  should  not  be  placed  nearer  to  each 


288  MINES. 

other  than  twice  the  line  of  least  resistance  of  the  heaviest 
charged  mines,  and  not  much  less  than  four  times  the  line 
of  least  resistance  of  the  smallest  charges.  Tliis  arrange- 
ment will  admit  of  a  comhinatioii  of  mines  in  two  tiers, 
the  line  of  least  resistance  of  the  lower  being  double  that 
of  the  upper,  the  chambers  of  which  may  be  so  ari'anged 
that  the  explosions  of  one  tier  shall  not  aft'ect  either  the 
galleries  or  the  mines  of  the  other.  Twice  the  line  of 
least  resistance  of  the  largest  mines  is  the  least  distance 
that  can  be  allowed  between  the  galleries,  in  order  that  the 
mines  of  the  lowest  tier,  which,  being  placed  near  one  gal- 
lery-, must  destroy  a  part  of  it,  shall  not  injure  those  par- 
allel to  it.  By  placing  the  galleries  at  this  least  distance 
apart,  the  branches  for  the  service  of  the  upper  tier  will  be 
us  short  as  possible,  attecting  thus  a  saving  of  time  and 
labor,  and  from  the  same  cause  the  galleries  on  any  one 
point  being  as  many  as  can  be  placed,  there  will  be  the 
advantage  that  some  one  of  the  galleries  will  be  service- 
able should  others  be  injured  by  explosions. 

791. ..The  galleries  and  branches  for  the  service  of  the 
different  groups  of  mines,  should  be  independent  of  each 
other,  so  that  there  may  be  no  confusion  in  the  service, 
and  that  no  group  may  be  rendei'ed  unserviceable  by  the 
destruction  of  the  communications  to  anotlier.  Tbe  same 
principle  should  be  attended  to  in  combining  the  different 
groups  of  mine  chambers. 

792... The  galleries  and  branches  should  never  present 
their  flanks  or  sides  to  the  globes  of  compression  of  the 
besiegers.  This  rule  leads  to  the  rejection  of  enveloping 
galleries. 

793... The  systems  of  countermines  proposed  by  most 
writers  on  this  branch  of  the  defence  are  generally  of  too 
complicated  a  character  to  admit  of  being  executed  at  a 
reasonable  cost,  and  they  require  for  their  service  not  only 
a  large  amount  of  powder  but  also  a  great  number  of 
miners. 

The  following  arrangement,  based  on  the  general  condi- 
tions just  laid  down,  has  been  proposed,  to  meet  in  a  sim- 


MINES.  289 

pie  and  satisfactory  manner  the  requisites  of  a  subterranean 
defence : 

Parallel  to  the  capital  of  the  demilune,  four  listening- 
galleries  are  run  out  to  a  distance  of  from  50  to  80  yards 
beyond  the  salient  of  the  covered-way.  The  ititcrval  be- 
tween these  galleries  being  twice  the  line  of  least  resist- 
ance of  the  heaviest  charged  mines.  If  we  take  this  line 
at  7  yards,  or  21  feet,  which  is  about  the  greatest  for  com- 
mon mines,  the  interval  of  the  galleries  will  be  15  yards. 
The  dimensions  of  the  listening  galleries  for  about  the  first 
20  yards  may  be  those  of  a  grand  gallery,  and  the  remain- 
ing part  may  be  a  common  gallery.  These  galleries  will 
depart  from  a  transversal  grand  gallery,  about  G  yards  from 
the  demilune  counterscarp,  which  will  serve  as  a  communi- 
cation between  them,  and  also  as  a  depot.  Other  transver- 
sals of  the  size  of  half  galleries  or  branches,  will  be  made 
at  different  intervals  for  the  purpose  of  ventilation.  This 
group  of  galleries  will  have  their  outlet  into  the  demilune 
ditch  through  two  galleries,  one  leading  from  each  ex- 
tremity of  the  transversal  grand  gallery.  To  flank  this 
group,  other  listening  galleries  will  extend  obliquely  out- 
ward from  the  two  outside  parallel  galleries.  To  serve 
the  mines  of  this  group,  a  series  of  ascending  branches 
will  lead  from  the  galleries  to  chambers  placed  midway 
between  the  galleries,  having  a  line  of  least  resistance  of  4 
yards.  This  will  place  these  chambers  at  about  8  yards 
from  the  two  adjacent  galleries.  Smaller  branches  may 
lead,  if  necessary,  from  these  last  branches  to  other  groups 
of  chambers,  having  a  line  of  least  resistance  of  2  or  3 
yards.  A  series  of  chambers  with  lines  of  least  resistance 
of  7  yards,  will  be  established  in  juxtaposition  with  each 
listening  gallery.  From  tiiis  arrangement  it  will  be  read- 
ily seen  that  ground  over  the  galleries  can  be  entirely 
broken  up,  and  that  the  successive  explosions  of  the  mines 
of  one  group  will  destroy  the  branches  and  galleries  which 
lead  to  them,  without  injuring  those  of  other  groups.  The 
object  of  this  disposition  is  to  blow  up  by  repeated  explo- 
19 


290  MINES. 

sions   tlic   2:roiiii(l    ovoi-  Avhidi   llio    oiicinv   Tnnst   nppi'oacli 
ujioii  ilic  (kMnilune  saliciit  place  ot"  arms. 

7U4...For  tlie  (lef'encc  ot"  the  otlior  portions  of  tlic  g-lacis 
of  tlio  (lemilnne  covered-way,  a  counterscarp  gallerv  of  tlio 
(liniensions  of  a  grand  gallerv  is  placed  between  tlio  two 
traverses  next  to  the  re-entering  place  of  arms;  a  listening 
gallery  extends  from  one  extremity  of  this  gallery  in  an 
oblique  direction  outward,  and  nearly  parallel  to  the  long 
branch  of  the  covered-way  crest  between  the  two  traverses, 
to  within  20  yards  of  the  foregoing  arrangement.  Other 
listening  galleries,  placed  15  yards  apart,  run  out  from 
the  main  one,  about  20  yards,  to  menace  every  point  of 
the  glacis  that  can  be  occupied  by  the  besieger's  works. 
The  groups  of  mines  for  these  galleries  may  l)e  arranged 
like  those  of  the  combination  in  advance  of  the  demilune 
salient  place  of  arms.  The  counterscarp  gallery  should 
have  two  outlets  in  the  demilune  ditch  ;  but  as  these 
might  compromise  the  safety  of  the  whole  arrangement, 
shoulil  the  besiegers  attack  the  covered-way  by  storm,  they 
must  be  walled  up  when  the  third  parallel  is  completed, 
and  the  communication  with  the  galleries  then  kept  up  by 
a  gallery  leading  to  the  main  ditch.  To  sup[)ly  the  main 
listening  gallery  of  this  group  with  air,  a  branch  should 
lead  to  it  from  a  point  of  the  deinilune  counterscarp  under 
the  traverse  next  to  the  one  of  the  salient  place  of  arms. 

795. ..Groups  of  galleries  and  mines,  similar  to  the  one 
in  front  of  the  demilune  salient  place  of  arms,  may  be 
arranged  for  the  defence  of  the  bastion  salient  place  of 
arms.  And  a  gallery,  leading  from  the  counterscarj)  of 
the  main  ditch,  may  be  made  for  the  service  of  a  group 
for  the  defence  of  the  glacis  of  the  re-entering  place  of 
arms. 

79G...To  defend  the  breaches  made  in  the  demilune  and 
its  redoubt,  a  gallery  may  be  made  under  the  ditch  of  the 
redoubt,  having  its  outlet  in  the  main  ditch;  this  gallery 
may  divide  into  two  branches,  one  leading  under  the  demi- 
lune breach  the  other  under  that  of  the  redoubt.  Ascend- 
ing branches  may  be  nuide  from  the  gallery  leading  to  the 


MINES.  291 

demilune  breach,  for  the  service  of  a  group  of  miues  to 
l)low  up  the  demihine  terreplein. 

797... Finally,  if  the  bastions  are  arranged  with  interior 
retrenchments,  a  disposition  similar  to  the  one  made  for 
tlie  defence  of  the  demilune  may  also  be  made  for  the 
defence  of  the  bastion  breach. 

798. ..As  the  air  in  tlie  galleries  of  mines  is  liable  to 
become  foul  from  various  causes,  some  mechanical  con- 
trivances and  chemical  methods,  by  which  the  vitiated  air 
can  be  removed  and  fresh  air  introduced,  have  to  be 
resorted  to  for  the  purpose  of  enabling  the  miners  to 
circulate  through  them  witli  safety.  Air  pumps,  bellows, 
and  artificial  drafts  procured  by  kindling  a  fire  at  one  of 
the  outlets  of  a  system  of  galleries,  are  the  ordinary  expe- 
dients by  which  this  object  is  attained. 

799.. .The  great  pecuniary  outlay  requisite  i"i.  establish- 
ing a  system  of  permanent  galleries,  besides  the  large 
corps  of  experienced  miners  and  the  extra  provision  of 
jiowder  demanded  for  their  efficient  service,  when  the  sys- 
tem embraces  any  considerable  extent  of  surface,  has  led 
engineers  to  consider  whether  the  end  proposed  by  subter- 
ranean means  of  defence  might  not  be  attained  by  some 
more  sim})le  expedients.  Since  the  application  of  galvanic 
currents  to  exploding  mines,  and  the  facilities  which  it 
affords  to  effect  this  at  very  considerable  distances,  it  lias 
been  ])rop()sed  to  substitute  isolated  shafts  for  galleries, 
jilacing  them  in  positions  most  suitable  to  attain  the 
besieger's  works.  These  shafts,  to  give  them  a  charac- 
ter of  permanency,  may  be  lined  with  masonry,  and  re- 
ceive a  stone  or  iron  cover  which  may  be  concealed  from 
view  by  placing  it  several  feet  l^elow  the  surface.  When 
wanted  for  service  the  shafts  are  charged  and  tamped  in 
the  usual  manner,  and  connected  with  a  galvanic  battery 
by  insulated  wire  conductors,  laid  sufficiently  far  below  the 
surface  of  the  ground  to  be  without  the  sphere  of  the 
besieger's  excavations  and  other  accidents. 


292  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 


glffarli  &  Science  of  |Jermancnf  ^'(Rorhfi 


FRENCH  MATERIALS. 

1... Under  tliis  head  are  ooiiiprised  the  materials  used 
hy  the  hcsiegers  for  revetenicnts  and  covers  against  tlio  fire 
of  the  defences. 

Fascines.  These  are  usually  made  18'  long,  and  9"  in 
diameter,  and  are  afterward  cut  into  suitahle  lengths  for 
the  purposes  to  which  they  are  to  he  applied. 

Pickets.  Those  used  for  securing  fascines  are  from  2'  to 
4'  long,  and  from  1  J"  to  If"  thick ;  those  for  setting  out  or 
tracing  the  works  are  18"  long  and  1"  diameter. 

Sap-fagots.  These  are  made,  like  fascines,  of  straight 
brush-wood  at  least  1"  in  diameter.  They  are  2'  9"  long, 
and  9"  in  diameter.  The  centre  stake  should  be  from  IJ" 
to  2"  in  diameter,  and  project  9"  beyond  one  end  of  the 
sap-fagot;  this  })rojeeting  portion  is  sharpened,  to  enable 
the  sap-fagot  to  be  planted  iirmly  in  the  ground  in  an 
upright  position. 

Gabions.  The  exterior  diameter  of  these  is  2',  and  the 
height  of  watling  is  2'  9".  They  are  made  with  seven  or 
nine  stakes,  which  project  6"  above  the  watling  at  top,  and 
are  pointed. 

At  the  siege  of  Sebastopol,  the  want  of  brush-wood  for 
the  watling  ol,"  gabions  led  to  the  introduction  of  the  com- 
mo!i  hoop-iron,  for  this  purpose,  which  had  served  to  secure 
the  bales  of  hay.  The  number  of  pickets  employed  for 
each  gabion  was  usually  thirteen.  It  was  found  that  these 
gabions  could  be  constructed  more  readily  than  the  ordi- 
nary kind  ;  that  they  were  not  much  heavier,  more  durable, 
and  in  all  respects  as  serviceable.  Since  then,  it  has  been 
proposed  to  use  simple  sheet-iron  cylinders,  of  suitable 
dimensions,  instead  of  the  brush-wood  gabion.     For  this 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  293 

purpose,  rcctangnlar  sheets  of  iron,  of  suitable  dimensions 
to  form  cylinders  of  the  same  hciglit  and  diameter  as  the 
ordinary  gabion,  are  prepared,  with  three  or  four  holes 
punched  near  and  parallel  to  the  shorter  sides  of  the  sheet 
to  secure  these  ends  with  wire  when  the  sheet  is  bent  into 
the  cylindrical  shape.  Besides  these,  two  other  holes  of 
larger  size  are  punched  toward  the  central  portion  of  the 
sheet,  so  as  to  be  diametrically  opposite  when  the  cylinder 
is  formed,  to  receive  a  picket  passed  through  them  which 
serves  as  a  handle  in  carr^-ing  the  gabion.  The  advantages 
of  this  description  of  gabion  are  greater  strength,  lightness 
and  durability  than  either  of  the  others  ;  oiiering  great 
facility  for  distant  transportation,  and  resisting  better  the 
blast  of  guns  when  used  for  revetting  the  cheeks  of  embra- 
sures, 

Sap-roli>ers.  This  is  a  large  gabion,  7'  6"  in  length, 
an<l  4'  4"  exterior  diameter.  It  requires  for  its  construc- 
tion fifteen  stakes,  each  from  1|"  to  2"  in  diameter.  After 
it  is  completed,  it  is  stuffed  compactly  with  fascines  7'  6" 
long.  The  sap-roller  is  sometimes  made  of  two  concentric 
gabions,  the  diameter  of  the  smaller  2'  6".  The  space 
between  the  two  is  compactly  stufi'ed  with  fascines. 

Sand-bacjs.  The  sand-bag,  for  the  revetement  of  batteries, 
when  empty  and  laid  flat,  is  2'  8"  long  and  1'  4"  wide ; 
those  used  in  the  construction  of  the  trenches  are  2'  long 
12"  wide. 

Blinda(;e-frames.  These  frames,  Tl.  10,  Fig.  1,  are 
composed  of  two  uprights,  or  stanchions,  of  5"  scantling, 
each  8'  6"  long,  and  pointed  at  both  ends  ;  and  two  hori- 
jiontal  pieces  of  the  same  sized  scantling,  each  3'  4"  long. 
The  horizontal  pieces  are  notched  upon  the  stanchions  at 
12"  from  each  end.  The  width  of  the  frame  from  out  to 
out  is  8'  4";  the  distance  between  the  horizontal  pieces 
from  out  to  out,  6'. 

An  oi(xilmr>/  sfaiichion,  Fig.  2,  with  a  projecting  piece,  is 
used  in  placing  the  blindage-frames. 

Oallery-framks.  The  arrangement  and  dimensions  of 
these  are  the  same  as  those  used  in  mining. 


294  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 


TRENCHES. 

2...TI1C  term  trench  is  applied  to  an  excavation  or  ditch 
made  b}'  the  heseicrers,  hy  means  of  which,  and  of  the 
earth  tlirown  from  it,  tlicy  are  enabled  to  obtain  speedy 
cover  from  the  tire  of  the  defences,  and  to  approach  tliem 
with  security. 

Trenches  arc  divided  into  two  principal  classes — the  par- 
allels and  the  approaches.  The  parallels  are  designed  as 
stations  for  troops  to  guard  the  trenches,  and  the  workmen 
employed  in  their  execution,  from  the  sorties  of  the  garri- 
son. The  approaches  serve  simply  as  covered  communi- 
cations which  lead  to  the  parallels,  and  toward  the  points 
of  the  defences  upon  which  the  attack  of  the  besiegers  is 
directed. 

The  general  direction  of  the  parallels  is  parallel  to,  or 
concentric  with^  the  line  connecting  the  most  salient  points 
of  that  portion  of  the  defences  attacked.  The  approaches 
are  run  in  a  zig-zag,  or  in  a  straight  line,  upon  some  or  all 
of  these  points. 

3. ..The  trenches  of  the  parallels,  PI.  10,  Figs.  3,  4,  5,  6, 
receive  a  width  at  bottom  of  10';  their  depth  in  front  is  3', 
and  in  rear  3'  6".  Two  steps,  each  18"  high  and  18"  wide, 
lead  from  the  bottom  of  the  trench,  on  the  front  side,  to 
the  natural  ground.  Tlie  reverse  of  the  trench  receives  a 
slope  of  45°,  or  else,  is  also  cut  into  two  steps.  The  steps 
in  front  are  alone  revetted  with  fascines.  The  trenches  of 
the  approaches,  PI.  10,  Figs.  7,  8,  are  8'  wide  at  bottom, 
3'  6"  deep  in  front,  and  4'  at  the  rear.  The  reverse  re- 
ceives a  slope  of  45°.  The  front  is  usually  nnide  with 
a  slope  of  2'  base. 

The  earth  from  the  trench  is  thrown  to  the  fi-ont  to  form 
a  parapet.  Tlie  general  height  of  this  parapet  is  nearly  5', 
its  width  at  the  base  about  18'. 

4. ..Simple  Trench.  When  the  parapet  is  formed  of 
earth  alone.  Figs.  3,  4,  7,  the  trench  is  termed  a  simple 
trench.     In  this  case  tlie  earth  of  the  parapet  is  allowed  to 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  20') 

take  its  natural  slope  on  the  side  toward  the  trench.  The 
step,  or  berm,  of  18",  between  the  foot  of  tlie  parapet  and 
the  trench  in  the  parallels  serves  as  a  baiupiette. 

Portions  of  the  parallels,  Figs.  4,  6,  from  20  to  30  yards 
in  length,  are  arranged  with  steps,  revetted  with  fascines, 
leading  from  the  trench  over  the  parapet,  to  enal)le  the 
troops  in  the  {larallel  to  debouch  from  it  against  a  sortie. 

The  direction  of  the  trench  is  laid  out  by  pickets,  con- 
nected by  wliitc  tape,  which  is  marked  off  into  lengths  of 
6'  by  short  pieces  attached  to  it.  The  trench  is  execnt(>d 
by  soldiers  of  the  line;  each  man  being  furnished  with  a 
pick  and  shovel,  with  which  lie  excavates  6'  in  length  of 
the  trench,  and  as  much  of  it  to  the  rear  as  may  be  assigned 
to  the  relief,  or  working  party,  to  which  he  belongs.  Aft(?r 
the  trench  has  received  its  general  width  and  depth,  the 
slopes  and  ste])s  are  finished  off  \w\th  the  assistance  and 
under  the  direction  of  the  engineer  troops. 

5. ..Flying  Sap.  Wlien  the  trenches  have  been  [»ushed 
forward  to  within  destructive  range  of  case  shot,  the  con- 
struction by  the  simple  trench  has  to  be  abandoned,  and  or.e 
which  will  afford  more  speedy  shelter  resorted  to.  This  is 
effected.  Figs.  ">,  8,  by  placing  a  row  of  ordinary  gabions 
in  juxtaposition,  along  the  direction  of  the  trench  ;  these 
being  filled  with  the  earth  from  the  trench,  the  parapet  is 
completed  b}'  throwing  the  remaining  earth  over  and  be- 
yond them.  This  process  is  termed  the  flying  sap,  from 
the  rapidity  witli  which  the  work  is  done.  It,  also,  is  exe- 
cuted by  troops  of  the  line,  eacli  man  bringing  two  gabions 
on  the  ground,  which  he  is  required  to  fill,  and  also  to 
complete  the  portion  of  the  trench,  in  the  rear  of  tliem, 
assigned  to  the  relief  to  wdiicii  he  belongs.  The  requisite 
height  is  given  to  the  parapet  either  by  heaping  up  the 
earth  above  tlie  top  of  tlie  gabions  or  by  placing  three 
ordinary  fascines  upon  the  galjions,  two  being  in  the  bot- 
tom course  and  the  other  on  top,  and  tlirowing  uj)  the 
earth  at  least  as  higli  ^s  the  top  fascine. 

In  positions  wliere  the  cartli  cannot  be  obtained  in  suffi- 
cient (juantity  to  afford   a  sjteedy  cover,  as  in  a  shallow 


296  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

stratum  of  soil  on  rock,  etc.,  two  rows  of  gabions,  placed 
in  juxtaposition,  may  be  used  for  the  flyinp;  sap. 

The  troops  for  constructing  both  this  and  the  simple 
trench  are  divided  into  three  parties,  or  reliefs.  The  tirst 
digs  the  trench  to  the  requisite  depth  and  to  the  width  of 
5' ;  the  second  widens  it  4'  6" ;  the  third  tinishes  what 
remains,  giving  the  requisite  slopes  to  the  front  and  rear. 

Remark.  The  dimensions  and  form  given  to  the  profiles 
of  the  parallels  and  boyaux  in  the  preceding  paragraphs 
are  those  used  in  our  own  and  the  English  sapper  practice. 
The  French  allow  usually  3'  3"  for  the  uniform  depths  of 
both,  and  4'  3"  for  the  height  of  parapet.  This  gives  a 
cover  of  7'  6"  in  the  trench,  which  would  seem  ample, 
whilst  it  gives  the  parapet  a  more  suitable  height  for  the 
convenient  delivery  of  the  fire,  if  the  troops  stationed  in 
the  parallels  are  called  upon  to  repel  a  sortie  in  this  way. 

6... Full  Sap.  The  full  sap,  Figs.  0,  10,  11,  is  resorted  to 
when  the  fire  becomes  so  destructive  that  the  flying  sap 
cannot  be  used.  The  trench  is  opened  and  pushed  forward 
by  engineer  troops  alone;  for  tliis  ptirpose  a  working  party, 
termed  a  h-if/ade,  of  eight  sappers  is  requisite.  The  bri- 
gade is  divided  into  two  equal  sections;  the  sappers  of  the 
first  section  dig  the  trench,  and  are  numbered  from  1  to  4, 
No.  1  leading.  The  other  four  are  termed  assistants ;  they 
bring  forward  the  materials,  and  assist  the  first  section 
in  all  the  necessary  operations. 

The  leading  saj)per,  No.  1,  is  provided  with  a  pick  and 
shovel,  and  wears  a  musket-proof  helmet  and  cuirass;  he 
works  on  his  knees,  being  covered,  on  his  side  toward  the 
defences,  by  the  parapet  of  the  trench,  from  which  he 
debouches,  and  in  front  by  a  sap-roller,  which  is  placed 
perpendicular  to  the  line  of  direction  on  which  he  is  to 
work,  and  rests  against  the  gabion  he  is  filling,  covering  it 
one  foot.  The  portion  of  the  sap  which  he  digs  is  21" 
wide  at  top  and  21"  deep;  it  receives  a  slope  of  4  perpen- 
dicular to  1  base  on  the  front,  andls  vertical  in  the  rear ; 
and  its  length  is  ;V.  So  soon  as  this  portion  is  finished, 
No.  2,  who  is  protected  in    all  respects  like  No.  1,  com- 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  297 

mences  to  widen  and  deepen  the  trench  8"  at  the  point 
from  which  No.  1  started,  and  follows  on  after  No.  1,  keep- 
ing always  5'  in  his  rear.  When  No.  2  has  pushed  for- 
ward 5',  No.  3  commences  and  enlarges  the  trench  in  each 
direction  7";  he  follows  on  also  A'  in  rear  of  No.  2,  but  as 
the  work  thnnvn  up  l\y  the  sappers  preceding  him  affords 
pretty  good  cover,  he  can  work  standing,  taking  the  pre- 
caution to  bend  forward  for  greater  security.  Finally,  No. 
4  begins  when  No.  3  has  got  on  P>',  and  deepens  and 
wndens  7".  As  he  is  well  covered,  he  can  work  in  an 
unconstrained  posture. 

Besides  the  shelter  given  b}'  the  gabions,  as  they  are 
successively  filled,  and  the  sap-roller,  the  further  precau- 
tion is  taken  of  driving  sap-fagots  along  the  berm,  at  the 
junction  of  the  gabions ;  these  are  successively  removed 
as  the}'  are  no  longer  requisite.  The  trench  fascines  are 
placed  upon  the  gabions  l)y  the  assistants,  and  the  remain- 
der of  the  trench  completed  b}-  working  parties  of  the  line, 
so  soon  as  the  brigade  of  sappers  have  proceeded  far 
enough  for  the  others  to  commence  without  hindrance. 

7..  Double  Sap.  This  sap,  Figs,  12,  13,  consists  of  two 
heads  of  sap  pushed  forward  by  two  brigades  working 
abi-east.  Its  object  is  to  form  a  trench  in  a  position 
exposed  on  both  sides  to  fire.  The  head  of  the  sap  is 
covered  by  two  sap-rollers  placed  end  to  end ;  a  bag  of 
wool,  or  a  short  sap-roller,  being  placed  at  their  junction 
for  additional  security.  The  distance  between  the  two 
rows  of  "fabions  is  13'.  The  earth  between  the  two  lines 
of  sap  is  removed  by  the  usual  W(U-king  jiarties,  as  in  the 
preceding  case. 

8  ..Half-double  Sap.  This  is  an  ordinary-  line  of  full 
sap.  Fig.  14,  pushed  forward  in  a  position  wliere  it  is 
necessar}'  to  give  temporary  cover  on  the  reverse  of  the 
trench  by  gabions  filled  with  sand-bags.  Tlie  distance 
l)etween  the  two  rows  of  gabions,  in  this  case,  is  only 
5'  0";  the  single  sap-roller  covering  in  front  this  intiM-val 
from  enfilading  fire. 

9. ..Defilement  of  Trenches.     The  position  given  to  the 


208  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

lines  of  the  parallel,  and  the  dimensions  ado})tcd  for  its 
treneli  and  parapet,  give  ani}>lc  cover  to  the  troops  in  it 
from  the  plunging  fire  of  works  having  anythitig  like  the 
usual  command.  But  in  the  zig-zag  approaches,  or  boyaux., 
as  the  line  of  tlie  trench  has  to  be  directed  toward  the 
defences,  it  is  necessary  either  to  defile  the  trench,  by 
i^ivins;  it  a  direction  such  that  the  fire,  comioff  over  its 
parapet,  will  not  have  a  plunge  sufficient  to  attain  a  man 
standing  in  the  reverse  of  it,  or,  when  this  cannot  be  done, 
by  placing  traverses  along  the  line  to  l)e  covered,  which 
shall  eflect  the  proposed  end. 

In  the  usual  cases  of  practice,  the  ground  on  which  the 
approaches  are  run  will  be  more  or  less  uneven,  and  this 
inequality  of  surface,  if  quite  appreciable,  will  demand  a 
corresponding  variation  in  the  line  of  direction  of  an  ap- 
proach, where  its  defilement  is  to  be  etfected  by  the  posi- 
tion given  to  it  with  respect  to  the  point  from  which  it 
may  be  attained  by  the  enemy's  fire.  In  most  cases,  how- 
ever, each  portion  of  the  line  of  the  trench,  corresponding 
to  the  changes  in  the  surface,  may,  without  any  very  great 
error,  be  regarded  as  lying  either  on  a  horizontal,  or  an 
inclined  plane ;  and,  in  the  latter  case,  the  plane  may 
either  rise  toward  the  dangerous  point  or  descend  in  the 
same  direction;  there  will,  therefore,  arise  three  cases  of 
defilement,  according  to  the  position  of  the  plane  on 
which  the  trench  is  run  with  respect  to  the  dangerous 
point. 

To  illustrate  these  cases,  let  the  approach  to  be  defiled, 
be  a  trench  constructed  with  the  flying  sap.  Now,  whe- 
ther the  ground  be  horizontal  or  inclined,  the  relative  posi- 
tion of  the  lines  of  the  profile  of  the  approach  should  be 
preserved  as  nearly  as  practicable.  The  vertical  height  of 
the  top  of  the  parapet — supposing  the  latter  no  highei- 
than  the  top  fascine — above  the  bottom  of  the  trench,  at 
the  reverse  side.  Figs.  15,  IG,  17,  will  then  be  8' 3";  and 
the  horizontal  distance  between  the  same  points  12'.  Now, 
in  order  that  a  man  standing  at  the  reverse  of  the  trench 
may  be  secure,  the  line  of  fire  of  the  enemy  should  not 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  299 

have  a  greater  plunge  than  6'  6"  ahovo  the  bottom  of  the 
trench  at  this  pohit.  This  Avill  limit  the  inclination  of 
the  line  of  tire  to  the  horizontal  drawn  through  the  top 
of  the  parapet  to  about  1  perpendicular  to  7  base,  or  an 
angle  of  4.  It  will  readily  be  seen  from  this  that  the 
line  of  the  trench  must  not  be  ran  so  near  the  dangerous 
point  that  the  line  of  tire  from  it,  passing  through  the  top 
point  of  the  parapet,  and  in  the  direction  of  the  i)rofile  of 
the  trench — that  is,  in  a  vertical  plane  containing  the  dan- 
gerous point,  and  perpendicular  to  the  horizontal  projec- 
tion of  the  line  of  the  trench — shall  make  a  greater  angle 
than  4;  and  that,  when  the  line  of  the  trench  satisfies  tliis 
condition,  it  will  be  defiled  by  its  position. 

To  FIND  THE  DEFILED  POSITION  OF  A  TRENCH  ON  HORIZON- 
TAL GROUND.  Let  D,  Fig.  18,  be  the  point  of  departure  of 
an  approach  leading  from  a  parallel,  and  0  the  most  dan- 
gerous point  of  the  defences  for  this  approach,  the  height 
of  which  above  the  parapet  of  the  approach  is  known.  It 
is  evident,  from  what  has  just  been  laid  down,  if  the  ap- 
[)roach  were  continued  on  beyond  the  point  C,  and  a  line 
with  an  inclination  of  -\  were  drawn  from  C  perpendicular 
to  the  direction  of  the  approach  and  through  the  top  of  its 
parapet,  that  a  man  standing  at  the  reverse  of  the  bottom 
of  the  trench  would  not  be  attained  by  this  lire:  but  as  the 
top  of  the  parapet,  or  interior  crest  of  the  approach,  is 
horizontal,  and  the  reverse  of  the  bottom  of  the  trcneh 
is  parallel  to  it,  it  is  farther  evident  that  the  plane  which 
passes  through  the  point  C  and  the  interior  crest  of  the 
approach,  will  pass  at  the  same  height  above  every  point 
of  the  reverse  of  the  bottom  of  the  trench  that  the  line  of 
4,  through  0,  does  above  the  point  G,  since  this  line  lies 
in  the  plane;  it,  therefore,  follows  that,  if  the  point  G  is 
defiled,  every  other  point  along  the  reverse  of  the  trench 
will  also  be  defiled.  To  construct  the  position  of  the  line 
DF  to  satisfy  this  condition,  describe  from  the  point  (.',  as 
a  centre,  with  a  radius  equal  to  seven  times  the  vertical 
height  of  C  above  the  parapet  of  the  approacli,  an  arc  of  a 
circle,  the  tangent  to  this  arc  from  D  will  l)e  the  required 
position. 


300  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

Note.  In  Fig.  18,  the  dangerous  point,  C,  is  18'  above 
the  horizontal  plane  of  the  trench.  The  reference  of  this 
plane  being  (0),  that  of  the  point  Cis  (18.0),  and  that  of 
the  interior  crest  of  the  approach  is  (4.25).  The  reference 
of  the  point  a  is  (11.0);  the  declivit}'  of  the  glacis  planes  ^^. 

10... To    FIND    the     defiled     POSITION    OF    AN    APPROACH    ON 

INCLINED  GROUND.  Let,  Fig.  18,  two  pUincs  of  a  glacis  in- 
tersecting in  a  ridge,  a6,  one  of  the  planes  rising  in  the 
direction  of  the  dangerous  point,  C,  and  the  other  falling 
toward  it,  be  taken  as  the  ground  on  which  the  trenches 
are  to  be  run ;  and  let  J.,  at  the  foot  of  the  plane  which 
ascends  toward  C,  be  the  point  of  departure  of  the  ap- 
proach. Now,  the  plane  being  produced  toward  C  may 
either  pass  above  it,  through  it,  or  below  it ;  in  either  of 
the  two  first  positions  it  is  evident,  if  the  interior  crest 
of  the  approach  were  directed  on  the  point  C,  that  the 
trench  would  be  defiled ;  for  no  line  of  fire  from  C  would, 
ill  either  of  these  cases,  have  a  plunge  into  the  trench,  and 
the  same  would  hold  true  if  the  plane  produced  passed  at 
a  distance  below  it  just  equal  to  the  height  of  parapet  of 
the  approach.  In  either  of  these  cases,  therefore,  to  defile 
the  trench,  it  will  onl}-  be  necessary  to  direct  its  interior 
crest  on  the  dangerous  point,  and  this  direction  may  be 
kept  until  the  approach  strikes  the  ridge  at  B. 

11... At  this  point,  as  the  plane  of  the  glacis  on  which 
the  prolonged  branch  of  the  trench  is  to  be  run  descends 
toward  6',  and  is  seen  in  reverse  by  its  fire,  it  will  be 
necessary  to  change  the  direction  of  this  branch  so  as  to 
withdraw  it  from  the  plunging  fire  from  C.  This  will  be 
eficcted  by  giving  this  branch  a  direction  such  that  a  line 
of  fire  from  C,  having  an  inclination  of  4,  and  being  con- 
tained in  the  profile  plane  of  the  trench  which  passes 
through  C  shall  clear  the  head  of  a  man  standing  in  the 
trench  at  the  reverse  side  ;  and  this  will  be  the  case  if  this 
line  of  4  passes  through  the  interior  crest  of  the  parapet 
and  6'  6"  above  the  l)ottom  of  the  trench  at  the  reverse. 
It  is  evident,  in  the  first  place,  that  this  will  be  true  for  the 
profile  plane  through  C.     Now,  since  the  line  of  the  inte- 


ATTACK  AND  DEFENCE  OP  PERMANENT  WORKS.  301 

rior  crest  and  the  line  of  4  intersect,  tliej  Avill  determine  a 
plane  which  passes  through  C,  and  in  which  all  the  lines  of 
fire  from  C  which  strike  tlie  interior  crest  are  contained. 
As  the  reverse  line  of  the  bottom  of  the  trench  is  parallel 
to  the  interior  crest,  and  as  the  plane  of  fire  in  question 
passes  at  6'  G"  above  that  point  of  the  reverse  line  of  the 
bottom  which  is  contained  in  the  profile  plane  through  C, 
it  follows  that  this  plane  also  passes  at  6'  6"  above  every 
other  point  of  this  reverse  line,  and,  therefore,  that  the 
direction  of  the  trench  which  fulfils  this  condition  will  be 
defiled  throughout  from  the  fire  coming  from  C. 

To  construct  this  position,  let  the  point  C  be  taken  as 
the  vertex  of  a  right  cone,  the  elements  of  which  make  an 
angle  of  i  Avith  its  base.  The  line  of  fire  of  4  will  be  an 
element  of  this  cone.  If  the  cone  be  intersected  by  a 
plane  parallel  to  the  one  on  which  the  approach  is  run,  and 
at  a  distance  above  it  equal  to  the  height  of  the  parapet, 
the  interior  crest  of  the  approach  must  intersect  the  curve 
cut  from  the  cone  by  this  plane ;  and,  to  satisfy  the  condi- 
tions imposed,  the  point  of  intersection  nmst  be  where  the 
projection  of  the  element  of  the  cone  is  perpendicular  to 
that  of  the  interior  crest,  as  these  are  the  relative  positions 
in  projection  of  the  line  of  fire  of  J  and  of  the  approach. 
To  construct  the  projection  of  the  curve  cut  from  the  cone, 
it  will  only  be  necessary  to  intersect  the  cone  and  plane  by 
equidistant  horizontal  planes,  and  to  find  the  projections  of 
the  corresponding  points  of  intersection  of  the  lines  cut 
from  the  two  surfaces  by  these  planes.  To  find  the  direc- 
tion of  the  approach,  join  the  point  of  its  departure,  B, 
with  0,  and  on  this  line  describe  a  semicircle;  the  point 
X,  where  this  semicircle  cuts  the  projection  of  the  curve 
cut  from  the  cone,  will  give  the  required  direction,  B  X,  of 
the  approach. 

A  like  construction  would  give  the  direction  of  an  ap- 
proach on  an  ascending  plane,  where  the  plane  passes  at  a 
greater  distance  than  the  height  of  the  parapet  below  the 
dangerous  point. 

12. ..It  will   be  noted  from  what  precedes  that  the  ap- 


302  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

preach  is  never  directed  within  a  dangerous  point;  for 
the  obvious  reason  that,  if  so  placed,  it  would  be  exposed 
to  reverse  fire  from  the  point.  If  it  should  happen  that 
the  direction  B  JT,  found  for  the  approach  in  the  preced- 
ino-  case,  would  bring  its  prolongation  within  a  dangerous 
point,  C,  on  the  left  of  the  ridge,  toward  which  the  plane 
ascends,  it  would  then  be  necessary  to  cliange  the  direction 
B  X  to  that  of  O  B  X\  and,  as  this  would  expose  the 
trench  to  a  plunging  fire  from  C,  it  will  be  ftirtlier  re- 
quisite either  to  deepen  the  trench,  or  to  raise  the  parapet 
higher,  to  cover  the  reverse  from  this  plunge. 

13... It  will  be  farther  noted  that,  at  the  point  of  depar- 
ture of  an  approach  from  a  parallel,  there  will  be  a  portion 
of  the  parallel,  o  j9  ^,  in  the  rear  of  the  trench,  which  will 
not  be  fully  covered  by  the  parapet  of  the  approach.  This 
portion  will  be  limited  by  the  line  of  fire  from  G  through 
0,  where  the  reverse  of  the  approach  cuts  the- interior 
crest  of  the  parallel,  and  by  the  reverse  prolonged  to  (y. 
To  secure  this  portion,  either  the  trench  of  the  parallel 
must  be  deepened  or  that  part  of  the  parapet  of  the  ap- 
proach be  raised,  which  is  intercepted  between  the  lines  of 
fire  from  C  on  'p  and  q. 

14... Defilement  by  Traverses.  When  the  defilement 
cannot  be  ett'ected  by  the  position  given  to  the  trench, 
resort  must  be  had  to  traverses.  Two  cases  present 
themselves  under  this  head:  one  in  which  the  reverse 
of  the  trench  is  exposed  to  a  very  slant  fire ;  the  other 
in  which  the  trench  is  pushed  forward  between  two  dan- 
gerous points,  and  is,  at  tlie  same  time,  exposed  to  an 
enfilading  fire. 

15... In  the  first  case,  Fig.  19,  the  trench  is  carried  for- 
ward by  means  of  the  half-double  sap.  So  soon  as  the 
head  of  the  sap  has  been  advanced  the  length  of  twelve 
gabions  beyond  No.  4,  a  short  end  of  sap,  termed  a  wing 
traverse,  is  commenced  in  a  direction  perpendicular  to  that 
of  the  trench,  and  run  out  until  it  intercepts  the  line  of 
fire  upon  the  point  of  departure  at  the  distance  of  twelve 
gabions  in  its  rear.     When  this  end  of  sap  is  completed, 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  303 

the  provisional  parapet  in  its  rear  can  be  taken  down  and 
the  trench  enlarged  to  its  proper  width.  In  this  way  the 
trench  is  successively  pushed  forward  and  enlarged,  until 
a  position  has  been  reached  where  it  becomes  necessary  to 
place  a  traverse  to  cover  tlie  trench  from  both  enfilading 
and  reverse  views.  These  traverses,  A,  A,  are  made  by 
changing  the  direction  of  the  trench  perpendicular  to 
that  of  the  original  lino,  and  continuing  in  this  new 
direction,  by  the  full  sap,  the  requisite  length  of  the 
traverse;  the  original  direction  is  then  resumed,  and 
continued,  by  the  half-double  sap,  a  sufiicient  distance 
to  leave  room  for  the  width  of  the  traverse  and  a  trench 
of  douple  sap ;  another  rectangular  turn  is  then  made,  by 
the  double  sap,  back  to  the  line  of  gabions  of  the  original 
trench,  and  the  original  direction  is  again  taken  up  and 
carried  forward  by  the  half-double  sap. 

The  traverses  A,  A  are  seven  gabions,  or  about  14'  in 
width.  Their  length  will  depend  on  the  position  of  the 
(hmgerous  point,  but  they  are  seldom  made  over  30'  in 
length.  Their  distance  apart  will  also  depend  on  the  com- 
mand of  the  dangerous  point.  The  portion  of  trench  be- 
tween any  two  traverses  must  be  perfectly  covered  by  the 
advanced  traverse.  As  a  practical  rule,  the  traverses  are 
not  placed  farther  than  25  or  30  yards  apart. 

The  portion  of  the  trench,  B,  in  rear  of  the  end  of  the 
traverse  is  covered  by  extending  sufficiently  far  to  the  rear 
of  it  an  end  of  trench,  C,  forming  a  wing  traverse,  to  in- 
tercept the  line  of  slant  fire. 

16. ..In  the  second  case.  Fig.  20,  the  trench,  A,  is  carried 
forward  by  the  double  sap,  until  the  [)oint  of  departure,  B, 
is  about  being  exposed  to  the  fire  coming  in  over  the  sap- 
rollers  ;  a  change  of  direction,  C,  at  right-angles  is  then 
made  by  the  full  sap,  to  the  right  or  left,  and  pushed  for- 
ward the  length  of  about  fifteen  gabions,  when  the  original 
direction,  D,  by  the  double  sap  is  resumed.  A  change  of 
direction  is  sometimes  made  botli  to  the  right  and  left  at 
right  angles  to  the  original  direction,  by  the  full  sap,  and 
pushed  to  the  length  of  twelve  or  fourteen  gabions.     Then, 


304 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 


from  the  extremities  of  these  branches,  a  direction  parallel 
to  the  original  is  taken  up  by  the  double  sap,  and  pushed 
on  until  the  point  of  departure  is  about  being  exposed, 
when  a  change  of  direction  is  made  at  right  angles  by  the 
full  sap,  and  the  two  branches  are  united  on  the  original 
direction,  E^  which  is  resumed  by  the  double  sap. 

17... Trench  Cavalier.     This  work  consists  of  a  parapet 
raised  on  a  mound  of  earth,  for  the  purpose  of  obtaining  a 

plunging  fire  on  the  covered- 
way.  The  mound  should,  in 
all  cases,  be  raised  so  high 
that  the  cavalier  will  have 
a  command  of  4^  feet  over 
the  crest  of  the  covered-way. 
The  position  of  the  cavalier 
is  shown  in  the  annexed  Fig. 
When  the  trenches  are  ad- 


fQ.  vanced  by  the  full  sap  nearly 
within  reach  of  grenades 
thrown  by  hand,  or  about 
30  yards  from  the  salient,  a,  of  the  covered-way,  a  circular 
portion  of  trench,  h  c,  is  formed,  to  embrace  the  production 
of  the  crests  of  the  salient ;  from  the  extremities  of  this 
circular  portion  the  sap  is  run  perpendicular  to  the  direc- 
tion of  the  crests,  to  a  distance,  c  d,  of  about  8  or  12  yards, 
so  as  to  enfilade  the  covered-way;  at  the  extremity,  d,  a 
wing  or  return,  d  e,  is  made  to  cover  the  part,  c  d,  from  the 
flank  and  reverse  fire  of  the  collateral  works;  this  part,  de, 
may,  in  some  cases,  be  arranged  nearly  parallel  to  the 
crotchets,  n  o,  of  the  covered- way,  so  as  to  give  a  fire  on 
them  ;  but  generally  it  serves  only  to  cover  the  branch, 
c  d,  as  has  been  explained. 

18. ..There  are  two  ways  of  forming  the  cavalier,  depend- 
ing on  the  nature  of  the  soil.  When  the  excavated  earth 
is  of  such  a  nature  that  it  can  be  easily  made  to  stand  at 
any  slope,  a  profile,  represented  by  Fig.  21,  is  preferred,  as 
requiring  less  time  and  materials.  After  having  laid  out 
the  position  of  the  cavalier  by  the  full  sap,  the  sappers 


ATTACK    AND    DEFENCE    OF    PERMANENT   WORKS.  305 

Widen  the  trench  6',  and  make  a  step  at  the  bottom  of  the 
trench  22-  in  height,  and  5'  6-  within  the  gabion  of  the 
parapet;  this  step  serves  as  a  phitform  on  which  the  sap- 
pers mount  to  level  the  earth   of  the  parapet  even   with 
the  hxscmes  on  top  of  the  first  gabion,  for  the  purpose  ot 
placing  a  second  tier  of  gabions,  which  is  placed  2^^"  be 
yond  the  first.     This  second  tier  is  filled  with  earth   and 
crowned  with  two  fascines,  and  the  mound  is  raised 'to  a 
level  with  the  fascines,  by  widening  the  trench  to  the  rear 
Ihe  earth  is  now  levelled  even  with  the  top  of  the  fascines 
and  a  third  tier  of  gabions  is  placed  just  on  the  outside  of 
the  second;  it  is  filled  with  earth,  crowned  with  three  f.s 
cines,  and  the  mound  is  raised  to  a  level  with  the  upper 
fascine.      This  top  tier  forms  the  parapet  of  the  work 
i.oop-holes  are  made  by  arranging  sand-bags  on  top  of  the 
parapet,  for  the  purpose  of  covering  the  heads  of  tlie  men 
whilst   ,n    the   act   of  firing.     As  the  successive  tiers   of 
gabions  are  placed,  steps,  revetted  with  fascines,  are  nnide 
to  lead  to  the  top;  these  steps  have  a  rise  and  tread  of  22"- 
the  top  one  serves  as  a  banquette. 

19...When  the  soil  excavated  is  loose,  a  cavalier  made  in 
tlie  manner  just  described  would  not  be  sufiiciently  firm. 
Ihe    following   construction    will    in    this   case   be   used- 
After  having  traced  out  the  cavalier  by  the  full  sap,  a  row 
of  gabions,  Fig.  22,  is  placed  in  the  bottom  of  the  trench 
along  the  foot  of  the  interior  slope;  this  row  is  filled  with 
earth,  and  crowned  with  two  fascines,  and  earth  is  filled  in 
between  it  and  the  interior  slope,  and  brought  to  a  level 
with  the  bcrm.     A  third  tier  of  gabions  is  phu-ed  on  this 
platform,  alongside  of  the  row  forming  the  i.arapet  of  the 
trench;  this  tier  is,  in  like  manner,  fi^lled  with  earth    and 
crowned  with  two  fascines.     The  second  tier  of  the  cava 
her  18  commenced,  by  placing  a  fourth  row  of  gabions  over 
the  joint  of  the  two  in  the  first  tier;  this   is   filled   with 
earth,  crowned  with  two  fascines,  and  the  mound  is  raised 
on  the  exterior  to  a  level  with  this  fourth  gabion.     A  fifth 
row  ,s  next  placed  alongside  of  the  two  in  the  first  tier 
filled  with  earth  and  crowned  with  two  fascines.     A  sixth 


306  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

is  tlieii  placed  alongside  of  tlie  fourth,  in  tlie  second  tier, 
and  arranged  like  the  preceding.  Finally,  the  parapet  is 
formed  on  this  second  tier,  by  placing  a  gabion  aboA-e  the 
joint  between  those  of  the  second  tier,  and  arranging  it  as 
in  Fig.  17.  The  steps  are  made  to  ascend  to  the  top,  by 
throwing  up  a  mound  of  earth,  on  the  interior,  against  the 
gabionade,  and  forming  the  surftice  into  steps  revetted 
with  fascines,  as  in  the  last  case. 


DESCENTS  OF  THE  COVERED-WAY  AND  DITCHES. 

20... Blinded  Descent.  When  a  trench  has  to  be  pushed 
forward  in  a  position  where  the  command  of  the  dangerous 
point  is  so  great  that  it  cannot  be  sheltered  from  the  plung- 
ing fire  by  traverses,  it  is  covered  on  the  top  and  on  the 
sides  by  fascines  and  earth  supported  by  a  framework,  and 
is  termed  a  blindage. 

But  this  method  of  obtaining  cover  is  principally  re- 
■quisite  in  trenches  which  descend  toward  the  dangerous 
point ;  like  the  passages  which  lead  from  the  trenches  on 
the  glacis  into  the  covered-way,  and  to  the  bottoms  of  shal- 
low ditches.  The  manner  of  forming  the  blindage,  Figs. 
23,  24,  is  to  set  up  a  row  of  blindage  frames  along  each 
side  of  the  trench  or  passage  ;  to  connect  the  two  rows  at 
top  by  like  frames  laid  across  the  line  of  the  trertch  ;  to 
cover  the  top  frames  by  fascines  and  earth ;  and  to  fill  in 
between  the  side  frames  and  the  sides  of  the  trench  with 
fascines.  The  trench  is  made  by  the  double  sap.  Its 
width  at  bottom  is  7'  6".  The  width  between  the  frames, 
6'.  The  frames  and  fascines  of  the  blindage  are  grad- 
ually placed  as  the  trench  advances,  the  latter  preceding 
the  former  about  b'.  The  work  is  begun  b}'  placing  an 
upright  frame  on  each  side;  the  two  are  next  connected  by 
a  frame  on  top,  one  side  of  which  is  lodged  on  the  top 
cross  pieces  of  the  upright  frames,  and  the  other  sup- 
ported by  two  auxiliary  frames  until  the  next  two  upright 


ATTACK  AND  DEFENCE  OF  PEllMANENT  WORKS.  307 

frames  are  placed;  the  fascines  are  then  thrown  over  the 
top  frame  to  the  depth  of  about  2',  and  these  are  covered 
with  earth  or  raw  hides,  to  prevent  their  being  set  on  iirc. 
Fascines  are  at  the  same  time  placed  in  on  the  sides. 

The  slope  given  to  the  bottom  of  a  blinded  descent 
should  not  be  greater  than  J.  When  the  descent  is  to  a 
covered-way,  Figs.  23,  24,  the  bottom  of  it  should  de- 
bouch into  the  covered-way  at  48"  below  its  terreplein; 
this  will  serve  to  determine  the  point  of  departure,  the 
slope  being  fixed,  which  should  be  5'  below  the  surface  of 
the  glacis,  so  that  when  the  blindage  is  put  up  at  this  point 
the  top  of  it  shall  not  be  above  the  level  of  the  parapet  of 
the  trench,  A  horizontal  landing  about  8'  in  breadth,  is 
made  at  the  entrance  of  the  blinchige  ;  and  this  is  con- 
nected with  the  bottom  of  the  trench  by  two  ramps  of  ^. 

The  point  selected  for  a  blinded  descent  into  a  covered- 
way  is  usually  at  the  end  of"a  traverse  :  as  the  traverse  will 
cover  the  outlet  of  the  blindage  from  a  plunging  fire  in 
front. 

21... A  descent  to  a  ditch  is  usually  by  blindage,  when 
the  depth  of  the  ditch  does  not  exceed  10'  or  12'.  For 
greater  depths  the  commencement  of  the  descent  is  by  a 
blindage.  Fig.  25,  which  is  continued  to  a  point  where  the 
bottom  of  the  descent  is  about  9'  below  the  surface  of  the 
ground  ;  here  the  l)lindage  in  tei'minated,  and  the  remain- 
der of  the  descent  is  made  by  gallery,  as  the  depth  of  the 
earth  above  the  gallery  will  be  sufficient  to  allow  the  exca- 
vation to  be  carried  on  without  trouble.  In  a  firm  soil, 
grand  gallery  frames  are  used  for  the  descent ;  in  a  loose 
soil,  common  gallery  frames.  The  construction  of  the  gal- 
lery is  the  same  as  for  a  mine  gallery. 

The  [toint  of  departure  of  a  ditch  descent  is  usually 
taken  at  only  al)out  2'  below  the  bottom  of  the  trench  ; 
the  usual  landing  being  made  at  this  point.  In  a  dry 
ditch,  the  bottom  of  the  descent  debouches  at  the  usual 
deptli  of  the  full  sap  below  the  bottom  of  the  ditch.  In  a 
wet  ditch,  it  should  come  out  about  15"  above  the  water 
level. 


308  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

l'A«8AGK8  OF  DITCHES. 

22. ..Dry  Ditch.  Tlic  i)assaL''o  of  a  drv  ditcli  is  notliini]j 
more  tliaii  a  full  sap,  which  leads  from  the  outlet  of  the 
descent  in  the  ditch  to  the  bottom  of  the  breach.  From 
this  point  the  trench  and  jiarapct  are  directed  up  the 
breach  to  the  scarp  wall,  which  forms  the  side  of  the 
breach  toward  the  dangerous  point.  The  only  precaution 
necessary  in  making  this  passage  is,  to  sink  the  trench  at 
the  outset  to  its  full  depth  of  43"  to  gain  secure  cover. 

23...Wkt  Ditch.  The  passage  of  a  wet  ditch  is  a  per- 
ilous and  difficult  operation  under  any  circumstances,  but 
particularly  so  when  a  strong  current  can  he  produced,  by 
the  besieged,  in  the  ditch.  The  metliods  usually  recom- 
mended are  to  form  a  dike,  or  bfidge  of  fascines  and  hur- 
dles, laid  in  successive  layers,  and  tirmly  connected  by 
pickets.  To  form  a  footing  for  the  dike,  a  grand  gallery 
is  excavated,  directly  behind  the  counterscarp  wall,  to  a 
distance  of  12'  or  15'  on  each  side  of  the  descent,  and  the 
earth  from  it  is  thrown  into  the  ditch,  through  the  outlet 
of  the  descent.  The  dike,  or  bridge  of  fascines  is  gradu- 
ally pushed  forward  from  this  point,  being  secured  in  the 
best  way  practicable  to  the  earth  thrown  into  the  ditch. 
The  sap})ers  who  carry  forward  the  head  of  the  dike  are 
covered  from  {]\c.  fii-o  of  the  dangerous  })oint  liy  a  musket- 
proof  mask  of  fascines  and  boards,  attache<l  to  a  raft  on 
which  they  work.  The  dike  should  be  from  12'  to  15' 
wide  at  top.  A  gabionade  parapet  is  [ilaced  on  it  toward 
the  dangerous  side.  It  is  formed  of  two  tiers  of  gabions, 
tilled  with  earth.  The  bottom  one  consists  of  two  rows  of 
gabions,  each  crowned  with  two  fascines — the  two  rows 
being  in  juxtaposition;  the  top  tier  is  a  single  row  crowned 
with  three  fascines.  The  top  of  the  dike  is  covered  by  a 
layer  of  earth,  and  the'  parapet  with  raw  liides,  to  pre- 
vent the  effects  of  incendiary  con)positions  that  might  be 
thrown  on  them.  Kaft-bridges,  on  barrels,  protected  by  a 
gabionade  [)arapet,  have  also  been  i)roposed,  })articularly 
where  a  strong  cui-rcnt  is  to  be  contended  with. 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  309 


BATTERIES. 

24... Enfilading  and  Counter-batteries.  These  batter- 
ies are  used  for  destroying  the  artillery  and  silencing  the 
fire  of  the  defences.  Positions  are  chosen  for  the  first 
from  which  the  terrepleins  of  the  faces,  that  bear  upon 
the  ground  on  which  the  parallels  and  approaches  are  laid 
out,  can  be  enfiladed  ;  the  second  are  so  placed  that  they 
can  bring  a  direct  or  a  slant  fire  against  the  embrasures  of 
the  points  to  be  silenced.  The  shot  from  the  former  is 
thrown  with  small  charges,  under  angles  of  elevation  of 
from  6°  to  9°,  so  as  to  ricochet  along  the  terrepleins, 
taking  the  guns  of  the  defences  in  flank;  the  latter  fire 
with  full  charges  directly  against  the  point  to  be  attained. 

25... As  the  efi'ects  of  both  direct  and  enfilading  fire  vary 
greatly  with  the  range,  positions  should  be  chosen  for  these 
batteries  as  near  the  defences  as  they  can  be  thrown  up 
without  too  great  a  sacrifice  of  life.  Positions  which  will 
give  ranges  between  300  3'ards  and  700  yards,  are  the  best ; 
nearer  than  300  yards,  the  workmen  would  1)e  exposed  both 
to  the  fire  of  musketry  and  case  shot;  beyond  700  yards, 
the  fire  upon  the  defences  becomes  very  uncertain.  The 
best  points  for  these  batteries  are,  therefore,  on  the  zone 
of  ground  occupied  by  the  first  and  second  parallels;  the 
former  l)eing  at  about  600  yards,  and  the  latter  about  300 
yards,  from  the  most  salient  points  of  the  defences. 

26. ..The  batteries  may  be  placed  either  within  the  par- 
allel, in  advance  of,  or  in  rear  of  it.  The  positions  usuall}' 
selected  are  from  20  yards  to  30  yards  in  front  of  the  par- 
allel ;  because,  if  placed  within  it,  there  might  be  mutual 
interference  between  the  service  of  tiie  batteries  and  that 
of  the  parallel ;  and  uidess  placed  some  distance  in  the 
rear  of  it,  the  }>arapet  of  the  parallel  might  obstruct  the 
shot  of  the  battery,  and  the  troops  in  the  trench  be  ati- 
noyed  by  the  fire. 

The  most  effective  positions  for  these  batteries  arc  in 
front  of  the  second  parallel ;  and  unless  the  fire  of  the  de- 


310  ATTACK  AND  DKFEXCE  OF  PKUMANEXT  AVOUKS. 

fences  its  very  (k'striu'tive,  it  will  bo  best  to  itlaeo  them 
there.  If  phiecd  in  front  of  the  first  parallel  it  will  be 
necessarv  to  sliift  the  most  of  tlicni  to  tlie  front  of  the 
second  ]»arallel  soon  after  the  latter  is  thrown  up.  For 
the  third  parallel,  and  the  approaches  leading  to  it  from 
the  second  parallel,  run  the  risk  of  being  attained  ])v  shot 
from  batteries  at  so  great  a  distance  in  their  rear  as  the 
first  parallel. 

27... The  site  of  tlie  platforms  of  the  batteries  may  either 
be  on  tlie  surface  of  the  natural  ground  or  sunk  below  it. 
In  the  latter  case,  tlie  battery  is  termed  a  stmhcii  bdtk'n/.  In 
the  former  case,  the  parapet  of  the  battery  is  obtained  from 
a  ditch  in  advance  of  it;  in  the  latter,  it  is  got  from  a 
trench  in  its  rear.  In  the  sunken  l>attery,  the  labor  of  con- 
struction is  less,  and  the  men  engaged  in  making  it  are 
placed  more  speedily  under  cover  than  in  the  other  kind. 
Sunken  batteries  can  only  be  used,  liowever,  when  the 
trenches,  or  other  elevated  points,  in  advance  of  the  bat- 
teries, wliicli  lie  in  their  field  of  fire,  will  not  intercept 
the  sliot:  and,  as  a  general  rule,  tliese  batteries  should  be 
placed  only  in  positions  where  their  field  of  fire  is  com- 
pletely unobstructed  by  the  trendies. 

28. ..The  interior  crest  of  an  eiiiihuliiig  batter}-  sliould  be 
nearly  }ier[)endicular  to  the  prolongation  of  the  line  to  be 
enfiladed;  and  be  so  placed  that  tlie  shot  from  all  the  guns 
shall  sweep  the  terreplein  throughout  its  entire  length. 
The  position  of  a  battery  that  will  satisfy  this  last  condi- 
tion can  be  readily  found,  as  it  must  evidently  lie  within 
the  angle  formed  by  producing  to  the  exterior  the  diago- 
nals ol"  the  terreplein  to  l)e  swept.  The  l)Gst  position  of 
the  guns  will  be  to  plaee  one  so  that  its  line  of  fire  shall  be 
nearly  on  the  prolongation  of  the  interior  crest  of  the  line 
enfihulcd,  and  the  remainder  on  that  side  (jf  this  one  on 
which  the  exterior  line  of  the  terreplein  prolonged  may 
fall. 

21*. ..In  a  couiitci'-battery,  tlie  interior  crest  should  be 
nearly  i»arallel  to  the  line  to  be  counter-battered.  A  j)Osi- 
tion  somewhat  obli(pie  to  the  line,  so  that  the  shot  of  the 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  311 

battery  may  enter  the  embrasures  obliquely,  is  also  a  good 
one  for  tearing  away  the  clieeks  of  the  embrasures,  and 
exposing  the  guns  of  the  defences. 

30... Whenever  a  position  has  to  be  taken  up  for  an 
enfilading  or  a  counter-battery,  in  which  the  direction 
that  can  be  given  to  the  interior  crest  is  very  ol)li(|ue  to 
that  which  it  ought  to  receive,  it  will  be  necessary  to  make 
tlie  embrasures  of  the  battery  with  a  corresponding  ob- 
liquity to  the  direction  of  the  parapet;  and,  to  avoid  the 
inconvenience  of  these  last,  it  will  be  farther  necessar}'  to 
break  the  interior  crest  into  an  indented  line,  to  allow  the 
muzzles  of  the  guns  to  be  run  the  requisite  distance  into 
the  embrasures  ;  placing  one  side  of  the  indent  perpen- 
dicular to  the  axis  of  the  embrasure,  and  the  other  parallel 
to  it. 

31... Enfilading  and  counter-batteries  are  usually  armed 
wnth  18  and  24-pounders,  and  8-ineh  howitzers.  The  fire 
of  the  guns  is  mainly  directed  to  destroy  the  artillery  of 
the  defences;  that  of  the  howitzers  to  sweep  the  covered- 
w^ays  and  ditches,  to  destroy  the  palisadings,  and  injure  the 
traverses  by  the  explosions  of  the  shells  that  may  lodge  in 
them.  As  a  general  rule,  there  need  not  be  more  than 
seven  pieces,  nor  should  there  usuall}'  be  less  than  three  in 
any  one  batterj';  the  number  depending  upon  the  bearing 
which  the  artillery  of  the  part  to  be  silenced  may  have 
niton  the  ground  on  which  the  works  of  the  besiegers  must 
be  placed.  The  batteries  should  be  as  far  asunder  as  prac- 
ticable, so  as  not  to  invite  a  concentration  of  the  fire  of  the 
defences  niton  jiny  point  l»y  the  accumulation  of  a  large 
number  (»f  pieces  on  it,  and  thus  multi[ily  the  chances  of 
loss  both  to  the  troops  and  materiel. 

32. ..In  computing  the  extent  of  front  of  a  battery,  D. 
11,  Fig.  26,  an  allowance  of  18',  estimated  along  tlie  in- 
terior crest,  is  made  for  each  piece,  and  6'  for  eacli  splinter- 
proof  gabionade  traverse,  one  of  wliich  is  placed  between 
every  two  guns,  when  there  are  more  than  tliroc  in  a  bat- 
tery. The  fianks  of  the  guns  are  covered  by  an  (.'pnulment 
tlirown   up  on   one,   or  both   extremities    of   the    parapet. 


312  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

The  Icngtli  of  the  epaulnieiit,  measured  along  its  interior 
crest,  may  he  from  20'  to  30'.  The  direction  of  tlie  epaul- 
mc'iit  willi  respect  to  the  i)arai)et  will  depend  on  that  of  the 
fire  of  the  defences:  as  a  general  rule,  the  interior  crest  of 
the  epaulment  should  make  an  angle  of  ahout  100°  with 
that  of  the  parapet.  When  the  platforms  are  on  the 
natural  surface,  the  earth  for  the  parapet,  epaulments 
and  traverses  is  taken  from  a  ditch  in  front  of  the  para- 
pet and  epaulments,  and  parallel  to  their  respective  direc- 
tions. A  narrow  ramp,  at  the  end  of  each  epaulment, 
leads  from  the  natural  level  to  the  bottom  of  the  ditch, 
and  serves  for  the  convenience  of  the  men  whilst  throwing 
up  the  battery.  A  trench,  of  the  ordinary  dimensions  of 
an  ajiproach,  and  defiled  from  dangerous  points,  leads  from 
each  extremity  of  the  battery  to  the  parallel  in  its  rear. 

33. ..If  the  embrasures  are  so  oblique  as  to  require  an 
indented  parapet,  the  side  or  face  of  the  indent,  through 
whi(;h  the  embrasure  is  pierced,  should  be  22',  and  per})en- 
dicular  to  the  axis  of  the  embrasure.  The  other  side,  or 
flank  of  the  indent  should  be  25',  and  parallel  to  the  axis  ; 
a  distance  of  only  7'  being  left  between  these  two  last 
lines,  to  give  all  the  thickness  practicable  to  the  portion  of 
the  merlon  that  forms  the  outer  angle  of  the  indent;  for  a 
like  reason  the  face  of  the  indent,  at  the  extremity  of  the 
batter}^,  sliould  extend  21'  beyond  the  axis  of  the  embra- 
sure. These  data  will  serve  to  estimate  the  total  length 
of  the  parapet.  Its  thickness,  estimated  from  the  inner 
angles  of  the  indents,  is  18'. 

84. ..The  profile  of  a  battery  w^ill  depend,  l)otli  for  its 
dimensions  and  form,  on  the  command  of  the  point  from 
which  it  can  be  attained,  and  on  the  position  of  the  surface 
of  the  ground,  on  which  it  is  laid  out,  with  respect  to  the 
defences. 

Where  tlie  site  of  the  battery  is  horizontal,  and  the  com- 
mand of  the  defences  over  it  is  within  the  usual  limits  of 
20'  to  30',  the  following  forms  and  dimensions,  Fig.  27, 
will  afford  ami)le  covei'  to  the  men  and  materiel  of  the  bat- 
tery, when  the  platforms  are  ou  a  level  with  the  natural 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  313 

surface:  Iloiglit  of  interior  crest,  7'  6".  Thickness  of 
parapet,  18'.  Interior  slope,  1-  Superior  slope,  j'^.  Ex- 
terior slope,  the  natural  slojte  of  the  earth.  The  same 
dimensions  and  forms  may  he  given  to  the  epaulments, 
except  the  distance  hetween  their  interior  and  exterior 
crests,  which  may  he  reduced  to  12'  when  the  direction  of 
the  epaulment  is  quite  ohli(pie  to  that  of  the  tire  of  the 
defences.  In  the  contrary  case,  this  distance  should  he 
18'.  The  depth  of  the  ditch  is  taken  at  5' ;  its  width  will 
he  regulated  by  the  (piantity  of  earth  to  he  furnished  for 
completing  all  the  parts  of  the  hatter}-. 

35... The  axes  of  the  embrasures.  Fig.  26.  are  18'  apart, 
except  at  the  points  where  splinter-proof  traverses  are 
placed — the  requisite  distance  at  these  points  being  24', 
allowing  6'  for  the  width  of  the  base  of  the  traverse. 
The  sill  of  the  embrasure  is  3'  6"  above  the  platform  for 
guns  mounted  on  the  ordinary  siege  carriage;  its  sole  is 
parallel  to  the  superior  slope.  The  mouth  of  the  embra- 
sure is  of  a  trapezoidal  form,  being  2'  wide  at  bottom  and 
3'  at  top.  The  splay  of  the  sole  is  obtained  by  giving  the 
sides  an  inclination  of  ^'^  with  the  axis.  The  top  line  of 
the  cheek  is  obtained  by  setting  off  along  the  direction  of 
the  exterior  crest,  from  the  jioint  where  the  side  of  the  sole 
cuts  it  in  projection,  one-half  the  vertical  distance  between 
these  two  last  lines,  and  joining  the  point  thus  found  with 
the  exterior  point  of  the  mouth  at  top. 

Embrasures  of  howitzers  may  receive  a  counter-slope, 
giving  the  sole  nearly  the  same  inclination,  from  the  sill 
upward,  as  the  least  angle  of  elevation  under  which  it 
may  be  required  to  aim  the  piece. 

36... The  parapet  of  the  battery  and  tlie  embrasures  are 
revetted  cither  with  gabions,  fascines,  or  sand-bags;  or 
with  a  combination  of  these. 

The  epaulments  need  not  be  revetted,  their  interior 
slopes  being  made  as  steep  as  the  earth  will  stand  at. 
The  gabion  revetement  is  the  firmest  and  most  durable. 
When   used  for  the  parajtet,  two  tiers  will  be  requisite. 

The  requisite  slope  is  given  to  the  gabions  of  the  first 


314  ATTACK  AND  DEFKXCE  OF  PERMANENT  WORKS. 

tier  by  placing  a  row  of  fascines  under  tlieni,  along  the 
foot  of  the  interior  slope.  Another  row  of  fascines  is  laid 
on  top  of  the  tier,  along  the  interior  sloi)e,  on  which  the 
gabions  of  the  second  tier  rest.  The  recpiisite  lieiglit  is 
given  to  the  parapet  eitlier  by  placing  sods  on  the  top  tier 
or  Ijy  earth  alone.  When  sand-bags  are  used  they  are  laid 
in  single  courses  along  the  interior  slope,  and  as  headers 
and  stretchers,  the  courses  breaking  joint.  To  give  the 
bags  greater  durability,  they  should  be  impregnated  with 
tar  before  l)eing  filled. 

It  has  been  found  that  raw  hides  will  preserve  the 
revetenients  of  the  cheeks  from  the  effects  of  the  concus- 
sion produced  by  the  firing.  For  this  purpose,  the  hide  is 
folded  with  the  hair  inward.  It  is  confined  to  the  top  of 
the  cheek  by  pickets  driven  through  it  into  the  merlon; 
and  at  the  mouth,  and  the  other  end  of  the  cheek,  by 
pickets  driven  into  the  revetement.  The  lower  end  is 
allowed  to  hang  loose. 

37... The  splinter-proof  traverses.  Fig.  28,  are  formed  of 
two  tiers  of  gabions.  The  lower  tier  consists  of  two  par- 
allel rows  of  gabions,  iind  is  S'  wide  at  the  base;  the  rows 
of  gabions  are  slightly  inclined  toward  each  other  at  top. 
The  upper  tier  also  consists  of  two  rows,  whicli  rest  on  two 
rows  of  fascines,  laid  on  the  first  tier,  the  gabions  leaning 
against  each  other  at  top.  The  gabions  and  the  space 
between  them  are  well  filled  in  with  earth,  which  is 
lieaped  above  the  top  tier.  The  traverse  may  be  from 
15'  to  18'  long.  A  passage-wa}'  of  2'  is  left  between  the 
parapet  of  the  battery  and  the  end  of  the  traverse. 

38... The  platforms  are  10'  6"  wide,  15'  long  in  the  clear, 
and  receive  an  upward  slope  of  7"  to  8"  from  the  hurter 
to  the  tail.  They  are  composed  of  5  sleepers,  each  15' 
long  and  5"  on  the  side;  of  12  planks,  each  10'  G"  long 
and  2"  thick;  of  2  ribands,  or  side-rails,  of  the  dimensions 
of  the  sleepers;  and  of  a  hurter.  The  sleepers  are  firmly 
imbedded  in  the  ground,  and  secured  by  stout  pickets  at 
their  ends.     The  i»lanks  are  clamped  between  the  side-rails 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  315 

and  outside  sleepers,  tliese  pieces  beiiii;;  connected  firnily 
either  In-  screw-bolts  and  nuts  or  Ijy  rack-lasliings. 

39... In  sunken  batteries,  the  same  length  of  interior 
crest  is  allowed  for  each  gun  as  in  the  preceding  case  ; 
but  when  the  battery  requires  splinter-proof  traverses,  an 
allowance  of  2G'  is  made  for  the  distance  between  the  axes 
of  the  guns  separated  by  a  traverse.  The  position  and 
length  of  the  epaulnients  are  also  determined  as  in  the 
preceding  case. 

40... The  trench  of  the  battery,  Fig.  29,  when  first  ex- 
cavated is  IG'  wide  at  bottom,  3'  deep  in  front,  and  2'  6" 
deep  in  rear.  The  front  is  cut  down  vertically  in  firm  soil, 
and  the  reverse  receives  a  slope  of  |.  The  interior  crest  of 
thp  parapet  is  4'  G"  above  the  natural  surface;  the  parapet, 
18'  thick;  the  interior  slope,  |;  the  exterior  slope,  }.  A 
bcrm  of  18"  is  left  between  the  parapet  and  the  trencli 
when  first  excavated. 

41... As  the  dimensions  above  given  to  the  trench  will 
furnish  earth  only  for  the  parapet,  that  required  for  the 
epaulmeut  is  taken  from  a  ditch  5'  deep  exterior  to  it;  and 
a  small  portion  of  ditch  is  made  exterior  to  the  parapet, 
and  opposite  the  position  of  each  splinter-proof  traverse,  to 
provide  the  earth  requisite  for  the  traverse,  and  which  is 
taken  from  the  trench.  The  epaulment,  if  exposed  only 
to  an  ol)li([ue  fire,  need  not  be  thicker  than  12'. 

42. ..The  embrasures  receive  the  same  form,  dimensions, 
etc.,  as  in  the  preceding  case. 

43... The  front  of  the  trench  is  revetted  with  fascines. 
To  put  up  this  revetement,  the  trench  is  widened  by  cut- 
ting away  the  front,  nearl}'  to  the  width  of  the  berm,  and 
almost  vertically.  This  will  admit  the  muzzles  of  the  guns 
to  be  run  well  into  tlie  embrasures. 

To  avoid  the  labor  and  expense  of  revetements,  it  has 
been  proposed  neitlier  to  revet  the  portion  of  the  trench 
bordering  tlie  epaulment,  nor  the  interior  slope  of  the 
epaulment;  but  to  leave  a  berm  at  this  part,  3'  wide, 
when  the  trench  is  in  course  of  construction,  and,  after- 
ward, to  give  both  to  tliis  portion  of  the  trench  and  the 


316  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

interior  of  the  epauliueiit  as  great  a  slope  as  the  earth  will 
stand  well  under. 

44. ..When  splinter-proof  traverses  are  requisite,  a  por- 
tion of  the  ground,  6'  wide,  on  which  the  traverse  is  to 
stand,  is  left.  The  traverse  is  made  hy  iirst  placing  two 
parallel  rows  of  fascines  at  5'  apart,  on  which  a  tier  of 
gahious,  also  of  two  rows,  rests ;  the  gahions  being  so  in- 
clined as  to  touch  at  top.  Eartli  is  tilled  in  the  gabions 
and  the  void  space  between  them,  and  heaped  up  above 
them  to  the  same  level  as  the  interior  crest.  The  sides 
of  the  trench  bordering  the  travei-se  are  cut  to  a  suitable 
slope,  and  revetted  with  fascines.  A  passage  of  2'  is  left 
between  the  gabionade  of  the  traverse  and  the  interior 
slope  of  the  parapet. 

45... To  provide  against  rainy  weather,  two  or  more 
holes  should  be  dug  at  such  points  of  the  trench  of  the 
battery  as  may  be  found  most  convenient  to  receive  the 
water  that  collects  in  the  trench ;  and  precautions  should 
be  taken  to  prevent  water  from  being  received  into  the 
trench,  either  through  the  trenches  leading  to  it  or  from 
the  natural  surface. 

46... The  powder  magazines  should  be  at  least  30'  in  rear 
(jf  the  parapet  of  the  battery.  The  ceiling  of  the  magazine 
should  not  be  more  than  a  few  inches  above  the  natural 
level.  The  interior  height  need  not  be  more  than  5'. 
The  width  may  be  6',  and  the  length  12',  in  the  clear. 
The  sides  of  the  magazine  may  be  formed  of  frames  and 
sheeting  boards ;  or  of  a  row  of  gabions  crowned  with  two 
courses  of  fascines.  The  magazine  is  covered  at  top  by 
splinter-proof  timbers,  6"x9",  laid  in  juxtaposition,  and 
covered  with  at  least  8'  of  earth,  both  on  top  and  on  the 
sides  toward  the  jiarapet.  A  passage  leads  into  the  maga- 
zine, oji  the  side  from  the  jjarapet  which  is  reached  by  one 
or  two  inclined  trenches. 

47. ..Mortar  Batteries.  There  are  two  kinds  of  mortar 
batteries  used  in  the  attack:  those  for  mortars  throwing 
shells,  and  those  for  mortars  throwing  baskets  of  stones, 
or  other  like  projectiles.     Besides  these,  there  is  the  Coe- 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  317 

horn  mortar,  wliich,  from  its  small  size,  may  be  placed  in 
any  nnocciipied  corner  of  the  trendies.  The  first  kind  of 
batteries  may  be  in  front  of  the  first  and  second  parallels, 
or  on  any  otlier  points  farther  back.  The  positions  chosen 
for  them  should  be  such  as  to  bring  as  great  a  portion  of 
the  defences  under  the  direction  of  their  fire  as  practi- 
cable, to  increase  the  chances  of  destructibility  of  each 
shell  thrown.  The  second  kind  are  placed  in  front  of 
the  third  parallel,  mainly  with  a  view  to  annoy  the  cov- 
ered-ways and  parts  adjacent. 

48... The  platforms  of  these  batteries  may  be  laid  on  the 
natural  surface,  in  w^hich  case,  the  same  forms  and  dimen- 
sions will  be  given  to  the  parapet  and  epaulments  of  the 
battery  as  in  gun  batteries ;  but  as  the  mortars  must  be  set 
back  from  the  parapet,  to  enable  the  shell  to  clear  the 
interior  crest  by  about  8',  a  revetement  will  not  be  neces- 
sary, and  the  parapet  may  receive  as  great  an  interior  slope 
as  the  earth  can  l)e  made  to  stand  under  firmly. 

49... The  front  of  a  mortar  battery  is  estimated  by  al- 
lowing 15'  for  each  mortar,  and  6'  for  each  splinter-proof 
traverse. 

These  Ijatteries  are,  however,  usually  sunk  below  the 
natural  surface,  since  several  feet  difterence  of  level  in  the 
position  of  a  mortar  will  have  but  little  eflect  on  the  range 
or  the  trajectory.  The  profile  suitable  for  such  positions, 
under  ordinary  circumstances,  is  the  following:  Width  of 
trench  at  bottom,  13'  6".  Depth  in  front,  3'  6".  Depth 
in  rear,  4'.  Reserve  slope,  i.  Front  slope,  2'  base.  Height 
of  parapet,  4'.     Thickness  of  parapet,  18'.     Berm,  1'. 

50... The  earth  for  the  epaulment  is  taken  from  an  exte- 
rior ditch  ;  and,  when  splinter-proof  traverses  are  required, 
portions  of  ditches  are  made  opposite  to  their  position,  to 
furnish  the  requisite  earth. 

51... The  platforms  of  mortars  are  7'  6"  long  by  6'  6" 
wide.  They  are  composed  of  two  ground-sills,  7'  6"  long 
and  6"  scjuare;  5  sleepers,  7'  6"  long  and  6"  square;  2  side- 
rails,  7'  0"  long  and  4"  square;  8  planks,  each  6'  6"  long 
and  4"  thick.     The  ground-sills  are  laid  horizontally,  and 


.318  ATTACK   AND  DEFENCE  OF  PERMAXEXT  WORKS. 

tirmly  imbedded  in  the  ground  at  4'  C"  apart,  and  trans- 
verse]}-  to  the  sleepers.  Upon  these  the  sleepers  rest;  eaeh 
being  confined  by  two  stout  pickets  near  each  end.  The 
planks  are  confined  to  the  sleepers  in  the  same  manner  as 
in  gun  platforms. 

52... Breach  Batteries.  Exposed  revetements  may  be 
breached  by  heavy  guns,  at  ranges  from  400  to  600  yards, 
and  batteries  thrown  up  in  such  cases  are  in  all  respects 
like  those  for  enfilading  or  counter-battering. 

53. ..Where  the  revetements  are  covered  from  distant  fire 
bv  the  crest  of  the  covered-way,  the  breach  batteries  must 
be  either  placed  on  the  glacis  or  on  the  terrepleins  ot 
the  defences,  at  points  where  no  obstruction  will  intervene 
to  prevent  the  fire  of  the  guns  from  being  directed  at  a 
point  of  the  wall  to  be  opened  low  enough  to  form  a 
breach  practicable  to  the  ascent  of  an  assaulting  column. 

In  either  of  the  latter  cases  the  batteries  must  be  sunk ; 
the  level  chosen  for  the  platforms  being  such  as  to  subserve 
the  object  in  view.  The  embrasures  in  these  cases  are 
usually  cut  out  of  the  parapet,  as  an  ordinary  trench  has 
generally  to  be  first  established  as  a  preparatory  step  to 
commencing  the  battery.  The  forms  and  dimensions 
adopted  for  other  sunken  batteries  will  apply  to  these 
cases,  with  such  modifications  as  may  be  demanded  by 
the  site  of  the  battery,  and  the  position  of  the  point  to 
be  attained  by  the  fire. 

When  a  breach  battery  is  established  cither  on  the  glacis 
or  upon  the  terreplein  of  a  work,  its  guns  will  generally  be 
exposed,  both  on  their  flank  and  rear,  to  the  fire  of  danger- 
ous commanding  points,  from  which  it  will  be  necessary  to 
cover  them  by  traverses.  The  number  of  traverses  and 
their  position  will  depend  u})on  the  command  and  position 
of  the  dangerous  |)oints.  To  cover  from  the  flank  fire,  if 
tlie  conniiand  of  the  dangerous  point  is  considerable,  like 
that  of  a  cavalier  retrenchment,  it  may  be  necessary  to 
place  a  traverse  between  every  two  guns,  or  even  between 
each.  The  traverses  used  in  such  cases  receive  a  thickness 
of  14',  or  seven  gabions,  like  those  for  covering  an  ordinary 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  319 

treiicli  from  an  enfilading  fire ;  their  length  will  depend 
upon  tlie  relative  positions  of  the  dangerous  point,  and  the 
exterior  point  of  the  hattery  to  be  covered  ;  their  height  is 
usually  not  greater  than  the  traverses  for  a  trench. 

When  the  reverse  of  the  battery  is  exposed,  it  will  gen- 
erally arise  fnun  the  salient  position  of  some  comparatively 
distant  point,  from  which  a  sh^it  fire  may  be  l)rought  to 
bear  on  this  part  of  the  batter^min  wliich  case  it  will  gen- 
erally be,  easy  to  cover  the  par^exposed  by  running  out, 
from  the  reverse  of  the  battery,  an  end  of  trench,  to  form  a 
wing  traverse  that  shall  intersect  the  lines  of  fire  of  the 
point  upon  every  part  exposed. 

54. ..The  guns  of  breach  batteries  should  be  so  placed 
that  the  direction  of  their  fire  may  be  as  nearly  perpendicu- 
lar as  practicable  to  the  line  of  wall  to  be  breached ;  and 
where  these  lines  are  oblique  to  each  other,  tlie  obli(iuity 
should  not  exceed  45°,  otherwise  the  eftect  of  the  shot  will 
be  gi-catly  diminished,  and  the  operation  retarded. 

Besides  the  breach  batteries,  it  will  be  necessary  to  place 
counter-batteries  on  the  glacis.  Their  object  will  be  to 
counter-batter  and  silence  the  artillery  of  those  portions  of 
the  defences  which  can  be  brought  to  bear  on  the  breach- 
batteries,  or  on  the  passages  of  the  ditches.  These  batter- 
ies will  usually  be  placed  on  the  prolongation  of  the  ditches 
of  the  defences.  Their  arrangement  will  be,  in  all  respects, 
the  same  as  that  of  the  breach  batteries. 


SIEGE  OPERATIOJS^S. 

55. ..The  operations  of  a  siege  are  usually  divided  into 
three  epochs.  In  the  first  are  comprised  the  investment, 
and  other  operations,  preliminar}-  to  breaking  ground 
against  the  work,  or  opening  the  trenches.  The  second 
comprises  the  labors  from  the  opening  of  the  trenches  to 
the  completion  of  the  third  parallel.  The  third,  the  subse- 
quent operations  to  the  rt-duction  of  the  work. 


320  attack  and  defence  of  permanent  works. 

First  Period. 

56. ..Investment.  This  is  the  first  active  operation  of  the 
besieging  force  ;  its  object  being  to  cut  oft"  all  communica- 
tion between  the  garrison  and  the  exterior,  to  prevent 
succors  of  every  kind  from  being  thrown  into  the  work,  to 
sweep  off  everything  in  its  vicinity  that  might  in  an}-  way 
be  serviceable  to  the  garrison,  and,  finally,  to  cover  a  close 
reconnoissance  of  the  defences  ])y  engineer  and  other 
officers. 

For  the  successful  attainment  of  these  ends,  the  invest- 
ing force,  which  is  mainh',  if  not  solely,  composed  of  cav- 
alry, should  move  upon  the  work  with  celerity  and  secrecy, 
and,  after  surrounding  and  securing  all  avenues  to  it, 
should  send  out  detachments  to  scour  the  environs  up  to 
the  very  gates  of  the  work,  if  practicable,  and  bring  off 
with  them,  or  destroy,  all  persons,  cattle,  provisions,  etc., 
met  w^ith.  A  chain  of  p.osts  and  sentinels  is  in  the  mean- 
time established  in  the  best  positions  to  prevent  all  access 
to  the  work,  or  egress  from  it ;  care  being  taken  to  select 
for  the  posts  points  which  are  not  exposed  to  the  artillery 
of  the  work,  or  are  beyond  its  range.  The  posts  occupied 
by  the  troops  during  the  daytime,  and  termed  the  daily 
cordon,  are  shifted  at  dark,  and  points  nearer  the  work  are 
taken  up,  to  form  the  nightly  cordon,  and  hem  it  in  more 
closely.  The  posts  and  sentinels  for  this  purpose  should 
be  pushed  as  far  forward  as  they  can  find  shelters  from  the 
musketr}'  of  the  defences  ;  and  under  their  protection  the 
reconnoitering  oflicers  should  spare  no  eftbrts  to  gain  an 
exact  idea  of  all  the  ground  exterior  to  the  work,  and  of 
the  character  of  the  defences. 

57... Posting  Besieging  Force.  The  main  body  of  the 
besieging  army,  with  the  engineer  and  artillery  siege-trains, 
follows  closely  upon  the  investing  corps,  to  prevent  the  line 
taken  up  by  the  latter,  which,  from  its  extent,  is  necessarily 
weak,  from  being  forced  either  by  the  garrison  or  by  strong 
detachments  from  without.  The  positions  for  the  camps  of 
the  various  corps  are  designated  by  the  commanding  gen- 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  321 

eral,  after  a  careful  reconnoissancc.  These  are  placed 
beyond  the  range  of  the  heavy  artillery  of  the  work,  with 
their  color  fronts  facing  from  the  work,  and,  as  far  as  prac- 
ticable, on  points  favorable  to  the  health  and  comfort  of  the 
troops,  and  the  defence.  Whenever  natural  obstacles  occur 
between  the  camps,  the\'  must  be  crossed  by  good  lines  of 
communication,  so  that  no  impediment  may  be  oflbi-ed  to 
the  speedy  concentration  of  the  troops  u})on  any  [)oint 
threatened  from  without. 

Besides  the  ])Ositions  taken  up  for  the  camps,  the  besieg- 
ing force  will  also  occupy  all  points  exterior  to  the  camps, 
within  cannon  range,  by  which  they  are  commanded,  secur- 
ing them  by  tield-works  of  sufficient  strength  to  subserve 
the  end  in  view. 

,'>8...Intrenciiments  of  Camps.  The  front  and  the  rear 
of  camps  are  also  secured  by  lines  of  field-works.  The 
exterior  works,  termed  the  Line  of  CircumvaUadon,  should 
form  an  unbroken  line  of  intrenchments,  composed  of  the 
most  simple  elementary  parts,  as  tenailles,  redans,  etc., 
with  a  slight  profile;  its  chief  object  being  to  prevent  suc- 
cors of  small  detachments  from  slipping  into  the  place. 
The  interior  line,  termed  the  Line  of  Countervallation,  is  com- 
posed of  detached  works,  which,  if  the  garrison  is  strong, 
should  be  in  defensive  relations.  The  main  points  which 
should  be  occupied  by  these  works,  are  the  principal  ave- 
nues to  the  defences,'  and  the  positions  selected  for  the 
parks  of  the  siege  train,  to  secure  these  points  from  the 
attempts  of  the  garrison,  and  to  render  the  entrance  of 
large  convoys  into  the  defences  impracticable. 

These  lines  are  placed  about  200  yards  in  front  and  rear 
of  the  camps. 

59. ..In  the  later  sieges  in  Europe,  lines  of  circumvalla- 
tion,  particularly,  were  seldom  resorted  to;  the  besiegers 
contenting  themselves  with  occupying  only  the  main 
points  of  their  position  by  field-works,  and  giving  the 
intervening  sj>ace  such  protection  as  could  be  aftbrded  by 
strong  patrols  and  posts.  This  departure  from  fi)rmer 
practice  arose,  in  most  cases,  from  the  want  of  strength,  of 
21 


# 


322  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

the  besieging  force,  and  was  frequently  attended  hy  the 
very  events  against  which  lines  are  chiefly  effectual  in 
guarding.  As  a  field  of  battle  against  a  succoring  force 
of  sufficient  strength  to  cope  with  the  besieging  army,  a 
position  taken  behind  a  line  of  circumvallation  is,  but  in 
rare  exceptions,  eligible — a  maxim  that  applies  to  all  ex- 
tended and  weak  lines;  and  in  almost  every  case,  where  a 
serious  eftbrt  has  been  made  against  such  positions,  it  has 
proved  successful,  and  has  entailed  heavy  loss  on  the  be- 
siegers. But,  it  must  be  repeated,  as  this  is  not  the  object 
of  these  lines,  they  are  not  open  to  this  objection  ;  and,  as 
they  have  been  found  serviceable  for  the  sole  purpose  to 
which  they  should  be  applied,  they  ought  to  be  thrown  up 
in  all  cases  where  the  means  of  the  besiegers  will  admit 
of  it. 

60... Preparations  for  Opening  the  Trenches.  Whilst 
the  besieging  force  is  occupied  in  arranging  and  securing 
their  camps,  a  portion  of  it  is  employed  in  preparing  the 
trench  materials,  establishing  the  parks,  and  getting  every- 
thing in  order  preparatory  to  breaking  ground  against  the 
defences.  At  the  same  time,  close  reconnoisances  and 
careful  instrumental  surveys  are  made  by  the  staff  corps, 
to  obtain  data  for  a  map  of  the  defences  and  their  envi- 
rons, with  a  view  of  drawing  up  a  plan  of  attack.  With 
this  object,  the  bearing. and  prolongations  of  the  faces  and 
capitals  of  all  the  defences  should  be  carefull}-  laid  down ; 
the  character  of  the  defences  on  every  assailable  point 
noted  ;  that  of  the  parts  bearing  on  these  points,  and  the 
nature  of  the  ground  over  which  they  must  be  approached. 

61... The  parks,  magazines  of  powder,  and  other  depots, 
are  placed  on  the  most  secure  points,  beyond  the  range  of 
the  heavy  artillery  of  the  defences,  and,  if  practicable, 
should  be  hidden  from  their  view.  The  points  selected, 
if  not  in  the  immediate  neighborhood  of  the  ground  on 
which  it  is  decided  to  open  the  trenches,  should  have  ave- 
nues of  easy  access  to  it,  for  the  transportation  of  whatever 
may  be  requisite  in  carrying  forward  the  works  of  attack. 

62... Point  of  Attack.     After  obtaining  all  the  informa- 


I 


ATTACK  AND  DEFENCE  OE  PERMANENT  WORKS.  323 

tioii  that  can  be  had  from  the  reconnoisaiices,  surveys  and 
other  sources,  the  next  object  is  to  decide  upon  the  portion 
of  the  defences  which  it  will  be  necessary  to  gain  posses- 
sion of  to  force  the  garrison  to  a  surrender;  this  portion, 
usually  embracing  one  or  more  fronts  of  the  enceinte,  with 
their  outworks,  and  any  advanced  works  that  may  be  con- 
nected with  them,  and  must  be  reduced  before  they  can  be 
assailed,  is  termed  the  Point  of  Attack.  It  is  in  the  choice 
of  this  point — a  decision  which  mainly  rests  with  the  com- 
manding officer  of  the  engineers — that  the  judgment  and 
skill  of  this  officer  are  shown.  In  making  this  selection, 
he  must  carefully  weigh,  not  only  the  relative  strength  of 
the  various  points  of  the  defences  wdiicli.  are  accessible,  but 
the  character  of  the  site  upon  which  the  trenches  and  other 
works  of  the  attack  must  be  laid  out,  and  the  facilities  of 
an  easy  communication  between  the  parks,  depots,  etc., 
and  the  point  selected. 

63... In  considering  the  strength  of  the  defences,  those 
parts  are  regarded  as  unassailable  by  the  ordinary  meas- 
ures of  an  attack,  which  border  upon  precipices,  marshes, 
a  water-course  that  cannot  be  forded,  or  are  protected  by 
works  on  inaccesiblc  points,  the  lire  from  which  sweeps 
in  Hank  and  reverse  the  ground  over  wdiich  the  trenches 
must  be  run.  Those  parts,  again,  are  considered  as  offer-  ^M^ 
ing  peculiar  difficulties  which  present  a  series  of  works,  in 
good  defensive  relations,  which  can  only  be  carried  in  suc- 
cession ;  or  w^hich  are  mined  ;  or  which  have  their  ditches 
arranged  for  a  play  of  water ;  dr  which  have  dry  ditches  of 
unusual  depth;  or,  finally,  where  the  works  to  be  carried 
are  displayed  on  a  right  line,  embracing  the  same  extent 
of  front  that  the  besiegers  caii  take  up  with  their  trenches. 
The  points  which  are  looked  upon  as  most  advantageous 
to  the  attack  are  those  in  which  the  general  combination 
of  the  works  form  a  salient  point  with  respect  to  the  rest 
of  the  defences  ;  as  a  point  so  situated  can  receive  but 
little  support  from  the  collateral  portions;  can  be  envel- 
oped by  a  line  of  trench  of  much  greater  extent  than  itself, 
along  which  positions  can  be  obtained  for  enfilading  and 


3"24  ATTACK  AND  PEFENCE  OF  PERMANENT  WORKS. 

otlicr  batteries,  the  fire  of  which  will  be  convergent  upon 
that  of  the  defences. 

64...  As  regards  the  site  on  which  the  trenches  and  other 
works  must  be  laid  out,  the  difficulties  presented  to  their 
construction  by  bare  rock,  marsh,  or  hard,  stony  ground, 
may  be  readily  appreciated,  as  cover  can  only  be  had  on 
the  two  first  by  bringing  the  earth  from  a  distance  to  form 
the  parapets,  dikes,  etc.,  and  on  the  last  from  the  labor 
requisite  in  digging  the  trenches,  and  the  additional  an- 
noyance and  injury  to  the  troops  from  the  fragments  of 
stone  scattered  in  all  directions  by  the  shot  of  the  de- 
fences. But,  besides  these  features,  there  are  others  less 
obvious  which  should  be  taken  advantage  of  or  be  avoided, 
as  favorable  or  otherwise  to  the  construction  of  the  works 
of  the  attack.  A  surface,  for  example,  which  slopes  or 
falls  away  toward  the  defences,  if  commanded  by  them,  is 
unfavorable  both  to  the  construction  of  trenches  and  bat- 
teries; as,  to  gain  sufficient  cover,  both  the  parapet  and 
trench  will  have  to  receive  dimensions  greater  than  under 
ordinary  circumstances;  and  the  defilement  of  approaches 
will  also  l)e  less  easily  effected.  A  surface  which  rises 
toward  the  defences  is  very  favorable,  both  for  gaining 
cover  speedily  and  for  defiling  with  advantage  the  ap- 
proaches ;  but  is  less  so  as  a  site  for  batteries  if  the  slope 
is  rapid.  An  undulating  surface  may  offer,  in  some  points, 
natural  covers,  and  be  at  other  points  favorable  as  sites 
for  batteries;  this  will  depend  upon  the  position  of  the 
undulation  of  the  surface  with  respect  to  the  fire  of  the 
defences.  A  ridge,  for  example,  leading  out  from  the  de- 
fences, whilst  it  would  present  a  cover  to  the  works  on  one 
aide  of  it  from  the  fire  of  the  defences  on  the  other,  would 
expose  the  trenches  on  the  other  side  of  it  to  a  plunging 
fire  from  the  same  points. 

A  narrow  valley,  similarly  placed,  would  be  very  unfavor- 
able, as  both  of  its  sides  would  be  exposed  to  a  plunging 
fire. 


attack  and  defence  of  permanent  works.         825 

Second  and  Third  Periods. 

65... Plan  and  Journal  of  the  Attack.  The  plan  of 
the  attack  is  necessarily  based  upon  the  character  of  the 
defences  of  the  point  of  attack,  and  of  the  site  upon  which 
the  approaches  and  other  works  of  the  besiegers  must  be 
laid  out;  and  by  this  term  is  understood  both  the  means  to 
be  used  at  the  successive  stages  of  the  operations,  and  the 
disposition  given  to  the  trenches  and  other  works.  The 
journal  of  the  attack  is  a  record  of  the  daily  operations  of 
the  besiegers;  and  is  also  a  method  in  use  among  engineers 
to  estimate  the  duration  of  a  siege,  from  the  opening  of 
the  trenches  to  the  reduction  of  the  work,  on  the  supposi- 
tion that  the  works  of  the  attack  can  be  carried  on  regu- 
larly, without  interruption  from  unforeseen  contingencies  : 
a  method  of  valuation  which,  as  it  is  based  on  the  time 
required  to  construct  a  given  amount  of  w(U'k,  as  deter- 
mined both  from  data  furnished  b}^  actual  sieges  and  the 
results  of  experiment  in  schools  of  practice,  may  be  relied 
on  as  an  approxinuition  as  close  as  the  case  admits;  and, 
when  applied  in  a  s})irit  of  fairness,  may  serve  as  a  test  of 
the  comparative  strength  of  difterent  combinations  or  syn- 
tems  of  permanent  works. 

66. ..The  general  disposition  of  the  works  of  the  be- 
siegers is  laid  down  on  the  map,  made  of  the  defences 
and  environs,  with  as  great  accuracy  as  can  be  insured  by 
surveys  carefully  made ;  and,  from  the  results  obtained  in 
this  wa}',  the  officers  charged  with  this  duty  are  enabled  to 
set  out  on  the  ground  the  necessary  points  by  which  those 
charged  with  directing  the  construction  of  the  works  are 
guided. 

67...  As  an  illustration  of  the  plan  and  jouriuil  of  attack, 
we  shall  suppose  the  point  of  attack  selected,  PL  12,  Fig. 
1,  to  be  an  acute  bastion  with  the  two  adjacent  demilunes; 
and  that  the  only  collateral  works,  the  fire  of  which  bears 
on  the  ground  over  which  the  trenches  must  be  run,  are 
two  collateral,  obtuse  bastions,  the  faces  of  which  cannot 
be  enfiladed,  owing  to  their  prolongations  falling  within 


326  ATTACK  AXD  DEFENCE  OF  PERMANENT  WORKS. 

the  salients  of  the  adjacent  demihines,  and  tlie  two  col- 
lateral demilunes;  making  in  all  one  hastion  and  two 
demilunes,  with  their  dependent  outworks,  which  must 
be  entered  by  breach  or  otherwise ;  and  two  bastions 
and  two  demihmes,  with  their  dependent  works,  the  fire 
of  which  must  be  kept  under. 

68.. ..The  approaches  will  be  pushed  forward  in  the 
direction  of  the  capitals  of  the  tliree  first  works;  and 
the  first  and  second  parallels  will  embrace  a  sufficient 
front  to  include  the  prolono^ations  of  the  faces  of  all  the 
works  bearino-  on  the  trenches,  aorainst  which  enfiladinfi: 
batteries  will  be  requisite. 

69... The  first  parallel  will  be  laid  out  at  600  yards  from 
the  most  advanced  salients  of  the  covered-ways,  and  paral- 
lel nearly  to  the  line  vrhich  c/)nnect8  these  points.  The 
approaches,  which  lead  from  it  to  the  depots  of  the  trenches, 
will  be  run  in  zig-zags  across  the  capitals,  each  not  over 
100  yards  in  length,  and  defiled  from  the  most  dangerous 
points  within  cannon  range. 

70. ..First  Night.  The  position  of  the  portion  of  the 
trenches  upon  which  the  besiegers  are  to  break  ground 
having  been  laid  out,  and  the  materials  for  the  work  hav- 
ing been  placed  in  order  for  distribution,  so  as  to  avoid 
all  unnecessary  delay  and  confusion,  the  workmen  are 
assembled  at  the  dei)ots  of  the  trenches  before  night-fall 
to  receive  their  implements.  The  men  selected  for  this 
duty  are  troops  of  the  line,  who  usually  take  their  arms 
with  them.  The  men  are  divided  into  working  parties, 
each  of  which  is  under  the  command  of  an  officer  of  the 
line,  and  they  are  marched  in  single  file  by  a  flank  and 
posted,  after  night-fall,  where  they  are  to  work  under  the 
direction  of  the  engineers. 

The  portion  of  the  trenches  opened  this  night  are,  usu- 
ally, only  the  approaches  that  lead  from  the  depdis  of  the 
trenches  to  the  first  parallel,  and  that  portion  of  this  par- 
allel which  embraces  the  capitals  of  the  point  of  attack. 
To  guard  the  workmen  from  sorties,  as  many  battalions 
of  the  line  as  may  be  requisite,  termed  the  guards  of  the 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  327 

trenches,  are  thrown  forward  about  30  paces  in  advance  of 
and  on  tlie  Hanks  of  the  men  wlio  open  tlic  first  })arallel. 
The  flank  companies  of  these  .battalions,  divided  into  sec- 
tions, cover  the  front  of  the  battalions,  and  are  posted 
about  30  paces  from  them ;  and  each  section  posts  two 
sentinels  at  about  the  same  distance  to  its  front.  The 
sentinels  keep  a  look  out,  kneeling-  on  one  knee ;  this 
remainder  of  the  troops  lie  flat  on  the  ground,  to  avoid 
the  fire  of  the  defences. 

When  the  working  parties  are  all  posted,  the  men  of 
each  lying  flat  until  all  are  ready  to  commence  the  work, 
the  order  is  given  to  rise,  ground  their  arms  a  few  paces  to 
the  rear,  and  break  ground. 

The  guards  of  the  trenches  keep  their  position  until 
near  dawn,  when  they  arc  withdrawn  and  take  post  in 
the  parallel,  which,  by  this  time,  will  be  nearly  excavated 
to  its  full  width. 

On  the  succeeding  day  all  that  remains  to  be  done  to 
the  trenches  opened  is  completed,  and  everything  is  got  in 
readiness  for  the  work  of  t^  coming  night. 

71. ..Second  Night.  The  parallel  will  be  extended  this 
night  to  embrace  the  prolongations  of  all  the  faces  to  be 
enfiladed,  and  some  100  or  150  yards  beyond  the  extreme 
points  so  determined.  A  large  square  redoubt  will  be 
constructed  at  each  extremity  of  the  parallel,  which  will 
be  armed  with  field  pieces;  and  an  epaulmcnt  for  cavalry 
will  be  tlirown  up  in  the  rear  of  each  redoubt;  the  object 
of  these  works  being  to  contain  troops  to  act  against  sor- 
ties made  on  the  flanks  of  the  parallel. 

The  zig-zag  approaches  are  pushed  about  150  3-ards  in 
advance  of  the  parallel.  The  positions  of  these  approaches 
are  determined  on  the  plan  b^-  setting  off  points  on  tiie 
first  parallel  at  30  yards  on  each  side  of  the  capital,  and 
drawing  lines  from  each  of  these  points  to  corresponding 
points  about  15  yards  on  the  side  of  the  ca}iital,  at  the 
salient  of  the  covered-way,  then  limiting  tlie  length  of 
each  zig-zag  of  these  lines,  the  direction  of  each  dc[»end- 
iiig   on  its   defilement.      To    cover   more    completely   the 


328  ATTACK   AND  DEFENCE  OF  PERMANENT  WORKS. 

reverse  of  eacli  zig-zag,  and  secure  it  from  positions  that 
niiglit  be  taken  up,  exterior  to  tlie  defences,  to  enlilade  it, 
the  zig-zag  in  advance  should  ha  i)rolonged  back  beyond 
the  limiting  lines  a  distance  of  10  or  12  yards  to  the  rear 
of  the  one  immediatel}'  behind. 

^' 72... Remark.  It  may  be  observed  here  that  by  running 
"l^proaclies  upon  three  capitals,  we  not  only  multiply  the 
lines  of  communication  between  the  parallels,  but  divide 
the  attention  of  the  besieged.  The  lines  of  the  capitals  are 
also  the  most  suitable  for  tliese  trenches  on  several  ac- 
counts :  first,  they  are  the  shortest  lines  between  the  paral- 
lels and  the  salients  of  the  defences;  second,  the  approaches 
along  them,  being  within  the  angle  formed  by  the  j)ro- 
longations  of  the  faces,  the^'  are  less  exposed  to  the  fire  of 
the  defences,  and  are  less  in  the  way  of  the  fire  of  the 
besiegers  than  in  any  other  position  ;  third,  in  this  position 
the  approaches  are  more  easily  defiled  from  the  collateral 
fire  than  in  any  other. 

By  confining  the  zig-zags  within  the  lines  drawn  tVom 
the  parallel,  and  converging  toward  the  salients,  the  front 
of  each  approach  is  gradually  contracted  as  it  nears  the 
salient,  and  oficrs  less  obstruction- to  the  fire  of  the  par- 
allel. 

7o...The  trenches  and  other  works  left  incomplete  at  the 
end  of  the  second  night  are  finished  on  the  following  day; 
and  this  rule  is  followed  throughout,' as  the  trenches  com- 
menced by  night  are  generally  in  a  suitable  state  by  dawn 
to  give  cover  to  the  workmen  and  troops,  and  can  be  occu- 
pied, and  what  remains  to  be  done  to  them  be  completed 
in  safety  by  day. 

74... Third  JSTight.  The  approaches  are  pushed  forward 
275  yards  from  the  first  parallel,  and  here  the  second  par- 
allel is  commenced;  a  small  portion  of  it  only  on  each 
side  of  the  approaches  being  opened,  in  which  to  lodge 
a  few^  troops  for  the  protection  of  the  workmen. 

This  parallel  is  of  less  extent  than  the  first,  embracing 
only  the  prolongations  of  the  faces  of  the  [toint  of  attack. 
It  is  usually  connected  with  the  first  parallel  by  a  defiled 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  329 

line  of  trench  at  each  of  its  extremities.  Its  distance  from 
the  first  is  determined  from  the  consideration  that  the 
workmen  emi)loycd  on  it  must  be  protected  by  the  guards 
of  the  trenches,  who  are  still  stationed  in  the  fii'st,  and 
who,  to  afibrd  this  j)rotection,  should  be  posted  where 
they  can  come  to  the  aid  of  the  workmen  before  the  garri- 
son can  reach  them  in  a  sortie. 

The  rule  here  observed  is  also  a  general  one.  The 
trenches  under  construction  never  in  any  case  being  ad- 
vanced ,so  far  that  the  guards  in  tlieir  rear  cannot  come 
u})  to  their  support  before  they  can  he  reached  b}'  a  sortie 
from  the  defences. 

75. ..Fourth  Night.  The  second  })arallel  is  entirely  laid 
out  on  this  night,  and  is  completed  on  the  following  day. 
The  guard  of  the  trenches  takes  post  in  the  parallel  as 
fast  as  a  part  of  it  is  finished ;  a  reserve  equal  to  about 
one-third  of  the  whole  l)eing  left  in  the  first  parallel. 

As  the  second  parallel  is  at  325  yards  from  the  salient 
of  the  place,  the  wc^-knien  are  much  exposed  to  the  fire 
of  grape  shot;  it  will,  therefore,  l)e  necessary  to  use  the 
flying  sap  in  its  construction, 

7G... Fifth  and  Sixth  Niohts.  Thus  far  the  works  of 
the  attack  have  been  pushed  tbrward  without  the  aid  of 
artillery,  but  beyond  the  second  i)arallel  the  fire  of  the 
defences  becomes  so  destructive  that  further  ])rogress  can- 
not be  made,  without  great  sacrifice  of  life,  until  it  is 
silenced.  To  ettcct  this,  enfilading,  mortar  and  counter- 
batteries  are  placed  about  30  yards  in  front  of  the  parallel. 
The  number  of  guns  in  each  battery  will  de})end  on  the 
im}iortance  of  the  face  to  l)e  silenced,  and,  according  to 
this  rule,  tlie  following  distribution  will  be  made: 

A  battery  of  8  pieces  will  be  erected  against  each  face 
of  the  bastion  of  attack.  A  battery  of  5  jiieces  against 
the  ric:ht  face  of  the  demilune  of  attack  and  its  covered- 
way,  and  one  of  7  pieces  against  the  left  face,  since  the 
fire  from  the  latter  bears  more  directly  on  tiie  approaches 
tljan  that  of  the  right  face.  As  the  two  collateral  bastions 
are  supposed  to  be  so  obtuse   that   their  faces  cannot  be 


380  ATTACK  AND  DEFENCE  OF  PERiMANENT  WORKS. 

enfiladed,  it  will  be  necessary  to  silence  their  fire  by  coun- 
ter-batteries. As  the  left  face  alone  of  the  bastion,  on  the 
right  of  the  one  of  attack,  has  a  direct  action  on  the  ap- 
proaches, a  counter-battery  of  5  pieces  is  erected  against 
it,  and  so  placed  as  to  obtain  a  slant  fire  into  its  embra- 
sures. With  regard  to  the  collateral  demilune  on  the  same 
side,  as  its  right  face  has  but  a  slight  bearing  on  the  ap- 
proaches, a  battery  of  3  pieces  will  prevent  this  face  from 
being  occupied  by  the  besieged ;  but  as  the  bearing  of  its 
left  face  is  more  direct,  it  will  be  necessary  to  establish  a 
battery  of  5  pieces  against  it;  this  last  battery  is  placed  in 
front  of  the  first  parallel.  Two  or  three  howitzers  form 
a  part  of  each  battery,  to  sweep  the  covered-ways  and 
ditches. 

The  mortar  batteries  are  placed  in  positions  where  they 
will  be  most  efi:ective,  which  is  usually  about  midway 
between  the  capitals  of  the  works  to  be  reached  from  them. 
About  4  mortars  arc  placed  in  each  battery,  an  allowance 
of  8  mortars  being  made  for  each  fj^nt  embraced  by  the 
trenches.  ,/,» 

The  mortar  and  gun  batteries,  the  fire  of  which  is  not 
obstructed  by  the  trenches  in  front  of  them,  are  suidv. 
The  platforms  of  the  others  are  on  the  natural  surface  of 
the  ground. 

Besides  these  batteries,  which  will  be  completed  on  the 
fifth  and  sixth  nights,  two  or  three  zig-zags  are  pushed  for- 
ward in  advance  of  the  parallel  on  the  same  nights,  if  the 
fire  of  the  besieged  is  not  too  destructive. 

77. ..Seventh  jSTigiit.  As  the  enfilading  batteries  will  be 
completed  and  armed  on  the  sixth  night,  on  the  following 
morning  they  will  all  open  their  fire  at  the  same  moment, 
and  by  night  the  fire  of  the  place  will  be  nearl}',  if  not 
entirel}',  silenced.  The  approaches  arc  then  pushed  for- 
ward, and  demi-parallels  arc  established  at  from  100  to  ir)0 
yards  in  front  of  the  second  parallel.  The  demi-parallcls 
may  be  from  100  to  200  yards  in  length,  and  have  a  return 
of  25  yards  at  their  extremities  to  cover  them  on  the  fiank. 
The  length  of  the  demi-parallel  should  be  so  regulated  as 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  331 

not  to  obstruct  tlie  fire  of  tlie  ricochet  butteries.  In  some 
cases  liowitzers  arc  placed  in  batteries  established  at  the 
extremities  of  the  demi-parallels,  to  enfilade  the  covered- 
ways;  but  as  the  demi-i)arallcls  are  within  good  musket 
range  of  the  covered-ways,  it  will  generally  be  better  to 
arm  them  with  infimtry,  the  top  of  their  parapet  being 
arranged  with  loop-holes  made  with  sand-bags,  to  cover 
the  marksmen  wliilst  in  the  act  of  firing. 

78... Eighth  Night.  On  this  night  the  approaches  are 
pushed  forward  by  the  flying  and  full  sap,  as  opportunity 
may  offer,  and  a  portion  of  the  third  parallel  is  commenced 
when  the  approaches  are  within  60  3-ards  of  the  most  ad- 
vanced salients. 

79... Ninth  Night.  Tlie  third  parallel  is  completed.  It 
should  present  a  less  develoiimont  than  the  second,  so  as  to 
be  fiaiikcd  by  it,  and  will,  therefore,  usually  embrace  only 
tlie  salients  of  the  point  of  attack.  Owing  to  this,  and  its 
having  to  receive  the  main  body  of  the  guard  —  the  second 
parallel  now  containing  only  the  reserve,  whilst  the  first  is 
used  only  as  a  depot  for  the  materials  and  to  receive  the 
wounded — the  third  parallel  is  made  two  or  three  feet 
wider  than  the  other  two. 

*  80...KEMARK,  With  the  completion  of  this  parallel 
begins  the  third  and  last  period  of  the  attack.  At  this 
[)oint,  the  works  of  the  besiegers  are  necessarily  contracted 
to  a  very  narrow  front,  and  present  but  little  more  develop- 
ment than  that  of  the  point  of  attack.  They  arc  now  upon 
the  immediate  ground  of  the  defences,  and  within  range"  of 
every  means  of  annoyance.  In  pushing  forward  from  this 
position  the  besiegers  are,  to  a  great  degree,  deprived  of 
the  assistance  that  they  hitherto  had  from  their  enfilading 
and  other  batteries,  as  the  position  of  their  trenches  on  the 
glacis  must  obstruct  this  fire  ;  they  can  no  longer  use  the 
zig-zag  approacli,  but  have  to  gain  ground  by  the  double 
sap,  and  soon  find  themselves,  as  their  works  advance 
toward  the  re-enterings,  the  enveloped  instead  of  the  en- 
veloping party,  and  liable  at  every  moment  to  have  their 
sappers  cut  off,  and  their  labors  stopped  by  sorties  in  small 


832  ATTACK   AND  DEFENCE  OF  PERMANENT  WORKS. 

parties.  It  is  at  this  stage,  then,  that  more  than  ordinary 
precautions  are  requisite,  not  only  to  prevent  retardation  of 
the  works,  but  to  avoid  unnecessary  sacrifice  of  life;  by 
preparing  all  possible  means  for  insuring  the  success  of 
each  stej),  and  by  not  advancing  on  one  until  tlie  last  taken 
is  perfectly  secure. 

81. ..Tenth  Night.  As  the  third  parallel,  PI.  12,  Fig.  1, 
from  its  position  on  the  glacis,  will  mask  the  fire  of  the 
ricochet  batteries  against  the  covered-way,  it  will  be  neces- 
sary to  establish  new  batteries  in  front  of  it,  to  dislodge 
the  besieged  from  this  outwork.  For  this  purpose,  stone- 
raortar  batteries  are  found  very  eft'ective.  These  batteries 
are  placed  at  about  20  yards  in  front  of  the  parallel,  and 
are  sunk.  A  battery  of  4:  or  6  mortars  is  })laced  on  each 
side  of  the  salients,  nearly  in  the  prolonged  direction  of 
the  covered-ways.  These  batteries  will  be  ready  to  com- 
mence their  tii'c  on  the  ct)vered-ways  on  the  morning  after 
they  are  begun. 

82... Storming  and  Crowning  the  Covered-way.  After 
the  completion  of  the  third  parallel,  preparations  are  made 
for  crowning  the  covered-way,  either  by  storm  or  by  gradual 
approaches.  In  the  former  case,  portions  of  the  parallel  are 
arranged  with  steps  to  enable  infantry  to  sally  from  it  on* 
the  covered-ways.  The  sappers,  with  all  the  necessary  ma- 
terials for  crowning  the  covered-way,  are  collected  in  the 
parallel.  At  a  })reconcerted  signal,  a  fire  will  be  opened 
from  tlie  stone-mortar  batteries,  and  all  others  that  are  still 
ertective,  against  the  covered-way  and  the  other  outworks. 
When  it  is  perceived  that  the  fire  has  produced  its  efiect  in 
clearing  the  outworks,  at  a  preconcerted  signal  it  will  also 
cease;  the  troops  will  sally  forth  and  carry  the  covered-way 
with  the  bayonet,  and,  after  gaining  possession  of  it,  they 
will  slieiter  themselves  as  they  best  can  behind  the  traverse 
from  the  fire  of  the  besieged.  Whilst  the^^  in  this  way, 
maintain  possession  of  the  covered-way,  the  sappers,  who 
follow  immediately  in  their  rear,  will  open  a  trench  about 
4  or  5  yards  from  the  crest  of  the  glacis,  around  the  salient 
place  of  arms,  as  far  as  its  two  traverses  ;  when  this  trench 


ATTACK   AND  DEFENCE  OF  PERMANENT  WORKS.  333 

will  afford  a  shelter  to  the  troops,  the}'  retire  from  the 
covered-way  into  it.  This  trench  is  afterward  connected 
by  suitable  communications  with  the  third  parallel. 

From  the  circumstances  nnder  wliich  tliis  operation  is 
carried  on,  the  probabilities  are  against  its  success  and  in 
favor  of  a  great  sacrifice  of  life  in  the  attempt,  if  the 
besieged  offer  a  vigorous  resistance  and  make  a  skilful  use 
of  the  means  still  at  their  disposal.  With  such  chances, 
therefore,  of  failure,  and  the  certainty  of  great  losses  even 
if  successful,  this  mode  of  attack  should  only  be  resorted 
to  in  some  contingency  where  the  success  of  the  sieo;e 
depends  on  the  time  saved  by  it. 

83... Eleventh  Night.  When  the  covered-way  is  to  be 
crowned  by  regular  approaches,  a  constant  fire  is  kept  up 
from  the  stone-mortar  batteries  so  as  to  render  it  untenable 
for  more  than  a  very  few  men.  A  trench,  termed  the  circu- 
lar i^lacc  of  arms,  is  now  formed,  by  starting  from  two  points 
of  the  parallel  at  30  yards  on  each  side  of  the  capital,  and 
pushing  two  branches  of  full  sap  to  unite  at  about  15  yards 
from  the  parallel,  on  the  capital.  From  this  ])oint  a  double 
sap  is  pushed  along  the  capital,  to  within  30  yards  of  the 
salients  of  the  demilune  covered-ways.  As  the  bastion 
covered-way  is  very  retired,  nothing  more  is  done  than  to 
form  the  circular  place  of  arms  before  it. 

84... Twelfth  Night.  The  trench  cavaliers  before  the 
demilune  salients  are  commenced,  and  the  sap  is  pushed 
forward  a  few  yards  on  the  bastion  covered-way. 

85... Thirteenth  Night.  The  trench  cavaliers,  which 
require  from  36  to  48  hours  for  their  completion,  will  be 
finished  on  this  night,  and  an  approacli  pushed  from  the 
stone-mortar  batteries  toward  the  re-entering  place  of  arms. 

8G... Fourteenth  Night.  The  besieged  being  now  driven 
from  the  covered-ways  by  the  fire  of  the  trench  cavaliers,  a 
double  sap  is  pushed  toward  the  salient  of  the  demilune 
covered-way  from  the  two  extremities  of  the  circular  trench 
connecting  the  trench  cavaliers.  These  two  saps  unite  at  4 
or  5  yards  from  the  crest  of  the  glacis. 

The  approaches  toward  the  re-entering  place  of  arms  are 
advanced  farther  on. 


334  ATTACK  AND  DEFENCE  OF  PERMANKNT  WORK?;. 

87. ..Fifteenth  Xight.  The  demilune  covered-way  is 
crowned  as  far  as  the  second  traverse.  The  approaches  on 
the  re-entering  place  of  arms  and  the  salient  of  the  bastion 
covered-way  are  advanced. 

88.. .A  fourth  parallel  is  begun  on  this  night,  commenc- 
ino-  opposite  the  first  traverses  of  the  demilune  covered- 
ways,  and  uniting  tlie  up}»rouches  pushed  toward  the  re- 
entering }»laces  of  arms. 

8>... Sixteenth  Night.  The  breacli  and  counter-batteries 
around  the  salient  place  of  arms  of  the  demilune  are  com- 
pleted and  armed. 

From  4  to  5  guns  will  be  placed  on  each  branch  of  the 
glacis  of  the  salient  place  of  arms,  in  the  prolongations  of 
the  demilune  ditch,  to  counter-batter  the  portions  of  the 
bastion  faces  which  bear  upon  this  ditch  and  the  covered- 
way,  and  prevent  this  lire  from  retarding  the  lodgments 
about  to  he  made  on  the  terreplein  of  the  salient  place  of 
arms  and  the  passage  of  the  ditch.  About  4  guns  are 
placed  in  a  battery  between  the  first  and  second  traverses, 
to  open  a  breach  in  the  left  face  of  the  demilune.  This 
breach  should  be  from  20  to  30  yards  in  width,  and  not 
extend  farther  toward  the  salient  thau  the  position  of  the 
pancoupe,  so  as  to  expose  as  great  an  extent  of  the  interior 
of  the  demilune  as  practicable. 

The  guns  in  these  batteries  will  require  cover  in  flank 
from  the  faces  of  the  bastions  and  their  cavaliers;  and  in 
rear  from  the  most  advanced  salients  of  the  works  still 
occupied  by  the  besieged. 

The  descent  into  the  demilune  covered-way,  commenced 
on  the  fifteenth  night,  behind  the  first  traverse,  is  finished  ; 
and  the  fourth  parallel  is  completed.  The  width  of  the 
fourth  parallel  is  the  same  as  an  ordinary  approach,  owing 
to  the  difficulty  of  defiling  it. 

These  batteries  will  be  completed  and  armed  in  24  hours 
after  the  crowning  is  commenced.  The  breach  will  be 
practicable  in  12  or  15  hours  after  the  fire  is  opened. 

90... Seventeenth  Night.  The  approaches  from  the 
fourth  parallel  are  pushed  forward  on  the  salients  of  the 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  335 

bastion  covered-way  and  tlic  re-entering  place  of  arms. 
The  crowning  of  the  deniihme  covered-way  is  gradnally 
advanced  and  a  h)dgment  is  made  on  the  terreplein  of  the 
demihiiu^  salient  phice  of  arms,  from  which  tlie  demilune 
ditch  can  he  swept  by  nuisketrv. 

The  descent  into  the  demilune  ditch  is  commenced  on 
this  night,  behind  the  traverse  of  the  salient  place  of  arms. 

91... In  advancing  the  sap  on  the  different  salients  of  the 
covered-way,  from  the  fourth  parallel,  care  should  he  taken 
not  to  pusli  forward  one  faster  than  the  others,  so  as  not  to 
offer  a  temptation  to  the  besieged  to  sally  out  on  the  head 
of  the  most  advanced,  to  cut  off  the  sappers.  Moreover, 
the  different  brigades  of  sappers  should  be  protected  b}'  a 
few  picked  men,  stationed  in  short  trenches  that  flaid<  tlu' 
direction  of  the  double  sap  as  it  is  pushed  forward  on  the 
salients. 

9'2...If,  owing  to  the  great  width  iA'  the  covered-way,  or 
to  the  small  breadth  of  the  demilune  ditch,  or  to  the  steep- 
ness of  the  glacis,  by  which  the  batteries  placed  along  its 
crest  would  be  very  much  exposed  to  a  reverse  fire  from 
the  collateral  works,  it  should  become  necessar}'  to  place 
the  43reach  and  counter-batteries  on  the  terreplein  of  the 
covered-way,  they  cannot  be  completed  and  armed  before 
the  seventeenth  or  eighteenth  night.  Although  the  bat- 
teries in  this  position  Avould  be  well  covered  from  reverse 
fire  by  the  crest  of  the  sjlacis,  and  from  a  flank  fire  by  the 
traverses  of  the  covered-way,  still,  they  would  I'ccjuire 
much  more  labor  to  establish  them,  and  would  be  more 
exposed  to  the  annoyance  of  grenades  thrown  from  the 
demilune. 

After  tlie  descent  into  the  demilune  ditch  is  commenced, 
it  is  steadily  carried  forward  until  it  arrives  at  the  point 
opposite  the  breach,  where  the  opening  into  the  ditch  is  to 
be  made  through  the  counterscarji  wall.  This  opening 
should  be  pierced  at  night,  and  the  precaution  should  be 
taken  to  run  a  small  gallery  along  the  back  of  the  wall,  on 
each  side  of  the  oi)ening,  so  as  to  place  a  few  men  to  fire 
through  loop-holes  made  in    the  wall,  for  the  purpose  of 


336  ATTACK   AND  DEFENCE  OF  PERMANENT  WORKS. 

defending  the  opening,  and  the  sap  pushed  across  the  ditch 
to  the  hreach. 

93... Eighteenth,  ISTineteenth  and  Twentieth  JSTights. 
The  approaches  from  the  fourth  parallel  and  the  crowning 
of  the  covered-way  are  pushed  forward  and  completed  on 
these  nights. 

It  will  seldom  be  practicable  to  establish  a  trench  cava- 
lier against  the  bastion  salient  place  of  arms,  owing  to  the 
reverse  tire  from  the  collateral  demilunes.  In  such  a  case, 
if  the  besieged  still  occu})}'  this  work  in  force,  so  as  to 
retard  the  progress  of  the  sap,  an  attempt  must  be  made 
to  dislodge  them  by  an  open  attack  of  a  small  party  of 
picked  troops,  or  else  stone-mortar  batteries  may  be  placed 
in  the  position  that  would  be  occupied  by  the  trench  cava- 
liers, by  means  of  which  the  besieged  may  be  driven  from 
this  part  of  the  covered-way. 

So  soon  as  the  bastion  covered-way  is  crowned,  two 
descents  are  commenced  into  the  main  ditch,  from  the 
trench  at  the  salient  of  the  covered-way. 

In  very  acute  bastions,  the  breach  and  counter-batteries 
along  the  bastion  covered-way  might  be  completed  on  the 
twenty-lirst  night.  But,  generally,  before  this  can  be  done 
the  demilune  must  be  carried,  as  its  fire  w^ould  take  these 
batteries  so  in  reverse  as  to  render  their  construction 
impracticable. 

94. ..Twenty-fifth  I^ight.  The  descent  into  the  demi- 
lune ditch  and  passage  of  the  ditch  may  be  effected  by  this 
night  at  farthest. 

Every  precaution  should  be  taken  to  prevent  the  be- 
sieged from  interrupting  this  passage.  The  passage  itself 
should  be  4  or  5  yards  wide  at  bottom,  to  afford  a  con- 
venient place  of  arms  for  the  troops,  and  it  should  be 
arranged  with  a  banquette  to  sweep  the  ditch  by  a  close 
musketry  fire. 

Besides  making  loop-holes  in  the  counterscarp  wall  to 
flank  the  passage,  it  will  also  be  well  to  push  forward  one 
or  two  zig-zags  in  the  ditch  itself,  and  place  a  small  party 
of  picked  men  in  them  to  repel  tlie  sorties  of  the  besieged. 


ATTACK  AND  DEFENCE  OF  PERMANENT   WORKS.  337 

95. ..The  breach  is  grained  possession  of  either  by  storm 
or  by  gradual  approaches.  The  former  will  be  resorted  to 
when  the  besieged  manifest  a  determination  to  keep  pos- 
session of  the  demilune,  in  force,  to  the  last  extremity.  A 
few  companies  of  picked  men  will  be  chosen  for  tins  ser- 
vice. All  the  materials  will  be  collected  at  hand  ^or 
crowning  the  breach,  and,  when  everything  is  in  a  state  of 
readiness,  a  warm  fire  will  be  opened  on  the  l)reac'h  and  on 
all  the  works  that  in  any  way  bear  upon  it.  At  a  precon- 
certed sio:nal  the  fire  will  cease,  and  the  assaulting  column, 
rushing  through  the  breach,  will  drive  the  besieged  from 
the  demilune,  and  then,  sheltering  themselves  as  the)'  best 
can  from  the  lire  of  the  other  works,  they  will  maintain 
possession  of  the  breach  until  the  sappers,  who  follow  in 
their  rear,  can  effect  a  lodgment  on  its  top. 

96... To  make  the  lodgment  by  gradual  approaches,  the 
sappers  will  push  forward  a  sap  from  the  foot  of  the 
breach,  over  the  ruins,  giving  it  such  a  direction  as  to  gain 
a  shelter  under  the  end  of  the  wall  that  remains  on  the 
side  of  tlie  breach  which  is  exposed  to  the  iii-e  of  the 
besieged.  A  few  picked  men  will  cautiously  mount  to 
the  summit  of  the  breach,  occupying  such  sheltered  points 
as  ma}'  be  found  at  hand,  for  the  purpose  of  covering  the 
sappers  whilst  at  work.  These  men  will  be  sustained  by  a 
detachment  posted  along  the  passage  of  the  ditch. 

97...TWENTY-SIXT1I  NiGiiT.  The  lodgment  on  the  breach 
of  the  demilune  being  effected  on  this  night,  the  breach 
and  counter-batteries  along  the  bastion  covered-way,  and 
against  the  redoubt  of  the  re-entering  place  of  arms,  can 
be  comi)leted  and  armed. 

A  breach  battery  of  4  guns  will  be  placed  along  each 
crest  of  tlie  bastion  covered-way,  as  far  from  the  salient 
as  room  can  be  had,  for  the  pur[)Ose  of  opening  as  wide  a 
breach  as  practicable  at  the  bastion  salient.  A  counter- 
battery,  likewise  of  4  guns,  will  be  placed  along  the  same 
crest,  and  in  the  best  }»osition  to  iire  in  the  prolongation  of 
the  main  ditch  and  silence  the  fire  of  the  enceinte  flanks 
opposite  to  them.  A  breach  battery  of  3  guns  will  also 
22 


338  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

1)0  }»laced  against  each  of  the  redoubts  of  the  rc-cnteriiig 
phice  of  amis,  to  open  them  on  their  faees  that  lie  adjacent 
to  the  demilunes. 

These  batteries  are  covered  in  flank  and  rear  in  the  same 
manner  as  those  against  the  demilune. 

,To  prevent  the  besieged  from  attempting  to  dislodge  the 
besiegers  from  the  demilune,  it  is  well  to  construct  a  trench 
across  its  terreplein,  from  which  the  ditch  of  the  demilune 
redoubt  can  be  swept  by  a  tire  of  musketry.  This  trench 
may  be  made  on  the  twenty-seventh  night. 

98. ..So  soon  as  the  demilune  breach  is  secured,  a  descent 
is  commenced  from  the  lodgment  on  it  to  the  ditch  of  its 
redoubt. 

This  descent  and  the  passage  of  the  ditch  of  the  redoubt 
will  take  until  the  thirty-second  night. 

In  the  meantime,  zig-zags  can  be  pushed  forward  in  the 
demilune  ditch  toward  the  glacis  of  the  single  caponniere; 
and  a  double  sap  be  formed  in  the  parapet  of  the  demilune 
itself,  to  overlook  the  ditches  and  to  a|)proach  the  cut  in 
the  demilune  face. 

A  descent  can  also  be  made  on  or  before  the  thirty- 
second  night  into  the  re-entering  place  of  arms,  and  a 
lodgment  be  effected  on  its  terreplein. 

99..  On  the  thirty-second  night,  miners  are  set  to  work 
at  the  scarp  wall  of  the  demilune  redoubt,  and  at  the  scarp 
and  counterscarp  walls  of  the  cut.  The  mines  may  be 
completed  and  fired,  and  the  lodgment  be  effected  on  the 
breaches  by  the  thirty-fourth  night;  at  which  time  the 
breach  in  tlie  redoubt  of  the  re-entering  place  of  arms 
is  also  carried. 

100... When  a  breach  can  l)e  opened  in  the  bastion  fiice 
through  the  opening  of  the  demilune  ditch,  the  zig-zags  in 
this  ditch  may  be  pushed  forward  nearly  to  the  extremity 
of  the  ditch,  and  the  passage  of  the  main  ditch  opposite 
the  breach  in  the  salient  be  effected  by  the  thirty-third 
night,  so  that  the  breaches  in  the  body  of  the  place,  and 
those  in  the  redoubts  and  the  cut  can  all  be  carried  on  the 
thirty-fourth.     I)Ut  when  a  breach  cannot  be  made  in  the 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKv'?.  339 

face  of  the  bastion  throngh  the  demilune  ditch,  and  it  is 
deemed  advisable  to  make  one  at  this  point,  it  will  be 
necessary  to  carry  tlic  outworks  first,  and  afterward  to 
push  forward  the  sap  to  crown  the  glacis  of  the  single 
caponni^re  in  the  demilune  ditch,  where  a  breach  battery 
of  two  guns  may  be  established;  at  the  same  time,  a  lodg- 
ment is  made  behind  the  bastion  covered  face,  and  ^a 
breach  battery  of  4  guns  is  established  there.  These 
labors  will  require,  for  their  completion,  until  the  thirty- 
seventh  niglit.  In  the  meantime,  lodgments  are  effected 
on  the  upper  and  lower  terrepleins  of  the  demilune  re- 
doubt, and  in  its  parapet,  to  overlook  the  main  ditch,  tlic 
double  caponnieres  and  the  tenailles. 

The  passages  across  the  main  ditch  are  also  completed, 
the  descent  to  the  one  nearest  the  shoulder  angle  being 
commenced  from  within  the  postern  of  the  redoubt  of  the 
re-entering  place  of  arms. 

101...TniRTY- EIGHTH  NiGHT.  Thc  lodguicut  on  the 
breaches  in  the  bastion  will  be  eftocted  on  this  night, 
and  a  descent  be  commenced  from  the  top  of  the  l)reach 
to  the  ditcli  of  the  cavalier. 

102... Thirty-ninth  and  Fortieth  Nights.  A  lodgment 
^^i\\  be  effected  on  the  bastion  terreplein,  and  a  brpach 
battery  of  4  guns  he  established  against  each  f^ice  of  tlio 
cavalier. 

The  breacli  in  the  cavalier  and  the  descent  into  the  ditch 
will  be  completed  so  tliat  the  final  assault  may  be  made  on 
the  forty-first  night. 

DEFENCE. 

The  object  of  this,  like  the  preceding  section,  is  to  give 
a  succinct  detail  of  the  operations  of  the  garrison  during 
the  successive  stages  of  the  attack,  supposing  the  works 
M'hich  they  occupy  provided  with  everything  requisite  for 
conducting  the  defence  vigorouslv. 

103. ..During  the  investment,  the  garrison  will  resort  to 
every  means  for  cutting  off  parties  of  the  investing  corps 


340  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

which  approacli  the  work  incautiously,  and  will  particu- 
larly endeavor  to  prevent  all  attempts  at  reconnoitring. 
About  one-third  of  the  garrison  will  be  kept  on  this  duty, 
taking  post  around  the  work  during  the  investment  and  as 
long  after  as  they  can  maintain  their  position  w-ithout  too 
fi-reat  danger. 

104. ..As  the  defences  at  this  period  have  no  other 
danger  to  apprehend  than  a  surprise,  and  nothing  to 
annoy  by  a  fire  but  reconnoitring  parties,  the  artillery 
will  be  so  posted  as  to  be  of  most  service  in  these  cases. 
Two  field  guns,  loaded  with  grape,  should  be  placed  in 
embrasure  on  each  flank,  and  one  or  two  more  on  the 
bastion  faces  to  sweep  the  ditches  of  the  demilunes  with 
grape,  to  frustrate  any  attempt  at  a  surprise;  and  two  or 
three  heavy  guns,  with  long  ranges,  should  be  placed  in 
barbette  on  each  of  the  salients  of  the  bastions  and  demi- 
lunes, to  keep  reconnoitring  parties  at  a  distance. 

105...  Whatever  precautions  may  have  been  taken  by  the 
besiegers  to  deceive  the  besieged,  relative  to  the  point  of 
attack  and  the  time  of  opening  the  trenches,  the  latter,  by 
keeping  a  strict  watch  on  all  the  moveriients  of  the  former, 
are  usually  enabled  to  ascertain  both  with  tolerable  cer- 
tainty, and  to  prepare  themselves  accordingly.  So  soon  as 
these  points  are  known,  the  garrison,  still  keeping  on  the 
alert  to  frustrate  all  attempts  at  surprise,  and  without 
changing  in  any  respect  the  artillery  already  in  position, 
will  place  all  the  disposable  pieces  in  reserve,  in  the  best 
positions,  on  the  fronts  of  attack  and  the  collateral  works, 
to  do  the  most  damage  to  the  laborers  and  the  guard  of 
the  trenches  before  they  are  placed  under  cover  in  the  first 
parallel.  Fire-balls  will  be  thrown  out  every  night  to  light 
up  the  ground  and  ascertain  the  position  of  the  laborers 
and  troops;  and,  so  soon  as  they  are  discovered,  a  heavy 
fire  of  grape,  etc.,  will  be  opened  on  them  from  all  the 
guns  that  can  be  brought  to  bear  on  their  position.  At 
the  same  time,  a  few  howitzers  will  keep  up  a  ricochet 
fire  in  the  direction  of  the  capitals  to  annoy  the  workmen 
at  the  approaches. 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  341 

After  an  interval  of  two  or  three  hours,  the  parapet  of 
the  parallel  will  be  proof  against  grape-shot,  and  then  a 
fire  of  balls  and  hollow  projectiles  will  be  commenced,  and 
directed  both  along  the  capitals  and  to  take  the  guards  and 
parallels  obliquely. 

106... Unless  the  srarrison  is  verv  stn^ns;,  or  the  besiegers 
show  a  want  of  proper  precantioTi  in  covering  their  laborers 
by  a  strong  guard,  sorties  cannot  be  made  at  this  period  of 
the  attack  with  much  jn-ospcct  of  success,  owing  to  the 
distance  of  the  parallel  from  the  defences.  The  most  that 
ought  to  be  attem])ted  will  be  to  make  some  charges  of 
cavalry,  to  cause  the  laborers  to  stand  to  their  arms,  and 
thus  retard,  for  a  short  time,  their  operations. 

107... When,  from  the  indications  without,  there  is  no 
longer  any  doubt  respecting  the  real  point  of  attack  se- 
lected, all  the  disposable  artillery  will  be  brought  forward 
and  placed  in  barbette,  in  the  best  positions  on  this  point 
and  the  collateral  works,  for  sweeping  the  ground  over 
which  the  trenches  must  be  pushed.  In  the  meantime, 
embrasures,  platforms  and  traverses  arc  prepared,  on  the 
most  suitable  positions  to  place  the  artillery  under  shelter 
so  soon  as  the  enfilading  batteries  are  completed. 

108. ..The  following  armament  may  be  taken  as  a  mean 
for  this  period  of  the  defence :  Eleven  pieces  in  the  bastion 
of  attack,  one  of  which  is  an  8-inch  howitzer,  firing  in  the 
direction  of  the  capital,  the  others  may  be  18  or  24-ponnd- 
ers,  five  being  placed  on  each  face. 

Seven  or  nine  pieces  of  like  calibre,  and  similarly  dis- 
posed, may  be  placed  in  the  cavalier  of  the  bastion. 

Eleven  pieces  will  be  placed  in  each  demilune  of  the 
attack,  one  being  an  8-inch  howitzer  to  fire  along  the  capi- 
tals, the  others  12  or  18-pounders,  six  of  which  arc  [)laced 
on  the  face  that  bears  on  the  ground  opposite  the  bastion 
of  attack ;  the  other  three  on  the  other  face. 

Five  pieces  of  heavy  calibre  on  the  faces  of  the  two  col- 
lateral bastions  which  bear  most  directly  on  the  trenches ; 
and  their  flanks  which  bear  on  the  bastion  of  attack  should 
each  receive  four  pieces  near  the  angle  of  the  curtain. 


o42      ATTACK  AND  DEFENCE  0¥   PEKJIANENT  ^VORKS. 

In  the  collateral  demilunes,  six  pieces  are  placed  on  the 
faces  alone  that  bear  on  the  trenches. 

Besides  the  preceding,  sixteen  8-inch  howitzers  should 
be  placed  in  the  covered-ways  of  the  point  of  attack  and  of 
the  two  collateral  fronts — two  beir-g  in  each  place  of  arms, 
to  tire  in  ricochet  along  the  capitals.  About  twenty  mor- 
tars should  be  distributed  along  the  curtains,  and  in  the 
demilune  redoubts. 

The  pieces  on  the  faces  which  are  enfiladed  should  be 
covered  by  gabionade  traverses,  placing  a  traverse  between 
every  two  pieces.  The  barbettes  in  the  salients  will  be 
partly  cut  down,  and  the  parapet  be  raised,  to  form  merlons 
and  embrasures  for  the  guns  at  these  points. 

109... An  uninterrupted  fire  should  be  kept  up  on  the 
parts  of  the  trenches  in  progress,  particularly  when  the 
besiegers  commence  throwing  up  the  enfilading  batteries. 
The  fire  should  be  concentrated  on  a  few  of  the  principal 
batteries  rather  than  scattered  over  all,  because,  by  delay- 
ing the  progress  of  these,  the  others,  if  the  besieged  act 
prudently,  wnll  not  open  their  fire  until  all  are  ready. 

110... If  the  approaches  are  not  well  defiled,  or  are 
directed  too  near  the  salients,  works,  termed  counter-a])- 
2)roaches,  may  be  made  from  the  covered-way  to  enfilade 
them.  These  works  are  usually  small  redan  batteries, 
placed  near  the  foot  of  the  glacis  to  receive  the  artillery 
in  reserve  not  required  for  the  immediate  defence  of  the 
work.  They  are  connected  with  the  covered-way  by  an 
ordinary  trench.  These  l)atteries  are  kept  armed  only 
during  the  day,  and  are  protected  by  small  detachments 
of  about  50  men,  to  secure  them  from  surprise. 

111... During  this  period,  the  engineer  ofificers  and  work- 
men are  employed  in  organizing  the  point  of  attack  for  a 
vigorous  defence.  The  covered-ways  are  palisaded  with 
care.  Tambours,  or  block-houses,  are  established  in  the 
salient  place  of  arms,  and  also  in  the  re-entering  places  of 
arms,  if  there  are  no  permanent  redoubts.  Similar  arrange- 
ments are  made  in  the  demilunes  which  have  no  redoubts; 
and  interior  retrenchments,  either  of  a  temporary  or  per- 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  340 

manent  character,  are  made  in  the  bastion  of  attack.     Easy 
coniiuunications  are  established  between  all  tlie  works. 

112. ..With  regard  to  the  portion  of  the  garrison  on  daily 
duty,  the  greatest  number  will  be  }>ostcd  in  the  defences 
more  immediately  threatened  by  the  besiegers.  About  40 
men  may  be  posted  in  each  salient  place  of  arms  of  the 
point  of  attack,  and  20  in  the  collateral  salients;  about  80 
in  each  re-entering  place  of  arms  of  the  same  point,  and  40 
in  each  of  the  collateral  ones.  Besides  these,  there  should 
be  a  detachment  of  about  10  men  in  each  demilune  of  the 
point  of  attack.  The  number  and  disposition  of  the  daily 
guard  will  of  course  vary  with  circumstances.  The  main 
point  to  be  attended  to  is,  that  no  part  of  the  work,  of  any 
importance,  shall  be  left  without  a  sutiicient  force  to  hold 
the  besiegers  in  check,  in  case  of  surprise,  until  support 
can  be  obtained  from  the  main  body,  which  last  should  be 
so  distributed  as  to  be  able  to  carry  succor  i)romptly  to  any 
part  threatened  or  attacked. 

113. ..So  long  as  the  besiegers  are  beyond  musket  range, 
the  guards  in  the  covered-way  have  only  to  keep  on  the 
alert,  and  to  send  forward  in  the  daytime  a  few  picked 
men,  who  take  advantage  of  any  shelter  to  approach  the  -^ 
trenches,  and  fire  on  the  workmen  or  guards  who  are 
exposed,  and  at  night  to  keep  out  patrols  to  scour  the 
ground  around  the  work;  to  annoy  the  workmen  when  an 
opportunity  offers,  and  to  prevent  the  approach  of  recon- 
noitring parties.  So  soon  as  the  trenches  are  pushed  for- 
ward within -musket  range,  an  unintermitted  warm  fire  of 
musketry  is  kept  up  on  the  woiknuii  ;iiid  guards  that  are 
exposed,  some  8  or  10  good  marksmen  being  placed  in  each 
salient  for  this  service. 

114. ..Sorties  may  be  made  with  more  chances  of  success 
when  ihe  besiegers  commence  the  second  parallel,  as  the 
guards  of  the  trenches  in  the  first  parallel  are  not  so  near 
at  band  to  protect  tlie  workmen  as  during  the  construction 
of  the  trenches  up  to  this  [loint. 

The  detachment  for  the  sortie,  consisting  of  3  or  400 
infantry,  will    sally  from    the  covered-ways  to  attack  the 


344  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

second  parallel  on  one  or  both  flanks,  and,  if  circum- 
stances favor,  ill  front.  When  the  workmen  are  put  to 
flight,  instead  of  }>ursuing  them  into  the  first  parallel,  the 
detachment  "will  form  in  battle  order  to  cover  a  party  of 
some  hundreds  of  workmen,  who  follow  in  rear  of  the 
detachment  whilst  thej  are  filling  up  tlic  trenches,  de- 
stroying the  implements,  and  setting  fire  to  the  gabions. 
The  working  party  will  be  covered  on  each  flank  by  a 
detachment  of  infantry  and  all  the  disposable  cavalry  of 
the  place.  When  the  guards  of  the  trenches  appear  in 
force  to  repulse  the  sortie  the  troops  will  retreat  slowly, 
without  compromising  their  safety,  and  will  endeavor  to 
draw  the  besiegers  in  the  pursuit  within  short  range  of 
case  shot,  a  fire  of  which  Avill  be  opened  on  them  so  soon 
as  the  retreating  troops  are  out  of  danger  from  it.  This 
operation,  if  successful,  may  be  repeated  several  nights  in 
succession  ;  the  best  moment  is  just  before  dawn,  when 
the  guards  of  the  trenches  are  fatigued  and  sleepy  with 
watching.  Although  the  chances  of  success  are  greater  at 
tliis  stage  than  at  the  opening  of  the  trenches,  still,  if  the 
besiegers  take  proper  precautions,  the  sortie  will,  in  all 
(^  probability,  prove  more  prejudicial  than  advantageous  to 
the  besieged. 

115... Before  the  besiegers  open  the  fire  of  the  enfilading 
batteries,  the  fire  of  the  defences  will  be  concentrated,  as 
bas  been  said,  on  the  principal  of  these,  and  will  lie  kept 
u[)  against  them  until  a  marked  efiect  is  observed  in  the 
■  fire  of  the  enfilading  batteries.  Only  one  gun  will  then  be 
left  between  each  traverse  on  the  faces  of  tbe  defences, 
the  otbers  are  withdrawn  and  kept  in  reserve.  The  guns 
and  howitzers  kept  in  battery  will  fire  steadily  upon  the 
heads  of  the  approaches  as  they  are  gradually  advanced. 

116, ..After  the  third  parallel  is  constructed,  the  hoAv- 
itzers  may  Ije  replaced,  with  advantage,  by  stone  and 
Coehorn  mortars,  firing  from  the  covered-ways  and  the 
red(»ul)tH  of  the  re-entering  places  of  arms.  Guns  will  be 
placed  in  embrasures,  to  fire  in  the  direction  of  the  ditches 
of  the  demilunes  of  attack  against  the  crowning  of  their 
covered-ways. 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  345 

117... At  this  stage,  the  musketry  fire  of  the  besiegers 
becomes  ver}-  destructive  to  tlie  artillerists  whilst  serving 
the  guns.  Strong  oak  musket -proof  blinds  should  be 
arranged,  to  mask  the  mouths  of  the  end)rasurcs  when 
the  guns  are  not  in  battery.  Blinds,  or  covers  of  timber 
and  earth,  under  which  guns  can  be  secured  from  projec- 
tiles that  would  reach  them  at  top  or  in  flank,  will  now  be 
serviceable.  A  few  guns  covered  in  this  wa}-,  and  placed 
in  the  salients  of  the  collateral  works,  to  obtain  a  reverse 
view  on  the  trenches  constructed  on  the  glacis,  will  prove 
a  serious  annoyance  to  the  sappers,  and  will  greatly  retard 
their  progress. 

118. ..The  troops  in  the  covered-ways  will  keep  np  a 
warm  fire  of  musketry  against  the  heads  of  the  sap,  and 
on  every  exposed  point.  The  men  firing  occupying  points 
where  they  will  be  best  sheltered  and  can  best  see  the 
leading  sappers.  A  few  mai'ksnien  will  also  occupy  the 
parapets  of  the  demilunes  and  the  redoubts,  to  keep  np 
a  fire  from  them,  but  only  during  the  day,  as  at  night  this 
fire  might  injure  the  men  in  the  covered-ways. 

The  greater  part  of  the  guards  of  the  covered-waj'  should 
now  be  withdrawn  at  night,  and  be  posted  in  the  demi- 
lunes and  redoubts,  so  as  to  expose  but  few  troops  if  an 
attack  by  storm  is  made. 

119. ..Although  sorties  in  large  bodies  will  seldom  prove 
successfid  after  the  second  parallel  is  finished,  those  made 
by  small  detaclinicnts  of  10,  20,  or  80  men  against  the 
head  of  a  sap,  or  other  work,  when  the  besiegers  are  ad- 
vancing beyond  the  third  parallel,  Avill  seldom  fail  if  con- 
ducted with  proper  precautions. 

This  method  of  annoyance  will  be  particularly  service-' 
able  during  all  the  subsequent  stages  of  the  defence,  as  the 
besiegers  cannot  now  have  at  hand  a  very  large  force. 

120. ..The  defence  of  the  covered-ways  will  be  regulated 
by  the  method  pursued  in  the  attack.  "When  the  latter  is 
made  by  gradual  ajiproaches,  the  troops,  with  the  excep- 
tion of  a  few  men  wlio  can  find  a  shelter  Itehind  tlie  short 
crotchets,  will    be    withdrawn   from   the    salient    places  of 


34G  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

uniis,  SO  long  as  tliese  are  annoyed  by  the  lire  of  the  stone- 
luortai's;  wLen  this  fire  ceases — which  takes  place  when 
the  sap  is  pushed  forward  from  the  third  parallel  —  the 
troops  again  enter  the  salient  places  of  arms,  and  renew 
their  fire  on  the  heads  of  the  sap,  directing  it  particularly 
against  the  sappers  working  at  the  trench  cavaliers.  When 
the  trench  cavaliers  are  completed  and  armed,  the  troops 
again  retire  from  the  salient  places  of  arms,  and  occupy 
the  traverses  and  short  crotchets,  where  they  maintain  their 
fire,  and  throw  hand  grenades  on  the  sap  when  it  comes 
within  their  range.  Stone  and  Coehorn  mortars  arc  also 
placed  behind  the  traverges,  to  annoy  the  sap,  etc. 

121... If  the  besiegers  are  observed  to  be  making  prepar- 
ations to  attack  by  storm,  no  more  troops  than  will  be 
required  to  line  the  parapet  of  the  covered-way  should  be 
posted  in  the  more  salient  parts,  and  they  should  maintain 
their  position  no  longer  than  is  necessary  to  give  the 
storming  party  one  voile}-  as  they  debouch  from  the  third 
parallel;  retreating  immediately  after  to  the  main  ditch,  or 
to  other  designated  points.  A  reserve  of  about  100  men  is 
posted  in  each  re-entering  place  of  arms,  to  cover  the  re- 
treat of  those  from  the  salients.  All  the  other  outworks 
are  lined  with  troo})s,  and  such  pieces  as  can  still  be 
brought  to  bear  on  the  glacis,  loaded  with  case  shot,  open, 
at  the  same  time  with  the  infantry,  a  deadly  fire  on  the 
storming  party,  which  is  kept  up  until  the  assailants  are 
either  driven  from  the  covered-ways  or  take  shelter  in  the 
trenches  constructed  by  the  sappers  along  the  crest  of  the 
glacis.  A  vigorous  sortie,  both  on  the  front,  the  flanks, 
and  tlio  reai-  of  the  storming  i)arty,  nuide  from  the  col- 
'  lateral  covered-ways,  will,  in  such  cases,  be  a  judicious 
operation. 

122. ..As  the  moment  for  crowning  the  covered-way 
approaches,  the  efforts  of  the  besieged  will  be  redoubled 
to  retard  the  works  of  attack.  Independently  of  the 
measures  already  laid  down,  the  besieged  will  arm  with 
artillery  the  flanks  which  bear  on  the  point  of  attack,  and 
will  construct  oblique  endjrasures  in  the  curtains,  to  sweep 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  347 

tlie  })Ositioiis  along  tljc  bastion  covered-ways,  wlierc  the 
besiegers  are  making  the  breach  and  connter-batteries. 
The  guards  of  the  covered-way  will  retire  toward  the 
re-entering  as  the  crowning  of  the  covered-way  advances, 
disputing  the  ground  foot  by  foot,  and  holding  possession 
of  each  point  until  the  besiegers  are  nearly  in  a  situation 
to  envelop  it  with  their  works.  The  stone  and  Coehorn 
mortars  will  be  removed  to  the  re-entering  places  of  arms, 
or  into  some  of  the  communications  in  the  rear  from 
which  a  fire  can  be  kept  up  on  the  trenches.  lu  line, 
every  possible  means  will  be  resorted  to  by  which  the 
sappers  constructing  tlie  breach  batteries  and  the  descents 
can  be  cut  ofl:'  and  their  labors  be  retarded. 

123... When  the  besiegers  have  established  themselves  so 
strongly  on  the  glacis  and  the  covered-way  that  sorties  in 
small  parties  cannot  be  made  without  too  great  risk,  a 
warm  tire  of  musketry  will  still  be  kei)t  up  on  the  trenches 
from  all  the  outworks,  and  the  besieged  will  wait  until  the 
descent  of  the  ditch  debouches  at  the  counterscarp  before 
renewing  the  same  game  of  sorties  in  small  parties.  A 
vigilant  look-out  will  be  kept,  to  ascertain  this  moment, 
and  so  soon  as  the  sappers  show  themselves,  every  effort 
will  be  made  to  cut  them  otit"  and  destroy  their  work,  by 
opening  a  tire,  both  of  artillery  and  musketry,  on  the 
debouche,  by  sorties  in  small  bodies,  and  by  throwing 
loaded  shells,  grenades,  etc.,  into  the  ditch. 

124. ..In  wet  ditches,  tilled  with  stagnant  water,  tlie 
besieged  will  resort  frequently  to  night  attacks  in  boats 
on  the  dike  or  passage;  and,  in  the  case  where  water  can 
be  suddenly  let  into  or  be  drawn  from  the  ditch,  chases  of 
water  will  be  used  to  sweep  away  the  l)esieger's  works. 

125... In  defending  the  breach  of  the  demilune,  the  be- 
sieged will  resort,  not  only  to  the  lire  of  its  redoubt,  l>ut 
will  erect  barricades  on  the.  right  and  left  of  the  breach, 
across  the  demilune  terrejjlein,  from  which  a  warm  tire 
of  musketry  will  be  poured  in  on  the  besiegers  whilst 
they  attempt  to  gain  possession  of  the  breach  either  l»y 
gradual  approaches  or  by  storm.     Small  mines,  or  b(>nd» 


348  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

fougasses,  sliould  be  prepared  at  the  summit  of  the  bread), 
to  be  exploded  so  soon  as  the  besiegers  gain  possession  of 
it.  The  top  of  the  breach  will  be  strowu  with  every  pos- 
sible obstacle  that  can  retard  the  progress  of  the  storm- 
ing party,  and  grenades,  thundering-barrels,  etc.,  will  be 
rolled  over  on  the  troops  whilst  mounting  the  breach. 

126. ..The  measures  for  the  defence  of  the  main  ditch 
and  of  the  breach  in  the  bastion  face,  differ  in  nothing 
from  those  resorted  to  for  the  demilune.  The  besieged 
will  make  everj'  eftbrt  to  keep  possession  of  the  ditch  to 
the  last  moment,  by  occupying  the  double  caponnieres  and 
the  teuailles,  from  each  of  which  works  a  steady  fire  will 
be  kept  up  on  the  besiegers  whilst  effecting  the  passage. 
Sorties  of  small  bodies  of  picked  troops  will  be  frequently 
made  under  the  protection  afforded  by  the  fire  of  the 
tenaille,  etc.  The  posterns  at  this  period  require  to  be 
guarded  with  peculiar  vigilance,  to  prevent  the  besiegers 
carrying  them  by  surprise,  and  thus  effecting  an  entrance 
into  the  interior  of  the  work. 

127 ...An  assault  of  the  breach  in  the  bastion  cannot  be 
opposed  by  the  bayonet  w^ithout  compromising  the  lines  of 
the  garrison,  unless  there  exists  a  good  interior  retrench- 
ment to  cover  the  retreat  from  tlie  breach ;  even  in  this 
case,  to  oppose  the  storming  party  with  the  bayonet  will 
be  an  operation  of  great  delicacy,  for  the  besieged,  if 
driven  back,  ma}'  not  be  able  to  effect  their  retreat  with- 
out being  so  mixed  up  with  the  assailants  as  to  render  it 
inqiossible  to  prevent  the  latter  entering  with  them  into 
the  retrenchments. 

128... Finally,  when  the  breach  is  effected  in  the  interior 
retrenchment,  the  besieged  may  offer  to  capitulate,  unless 
they  are  still  able  to  protract  the  resistance  a  day  or  two 
by  organizing  temporary  defences,  and  by  placing  the 
houses  in  tlie  rear  of  the  retrenchments  in  a  defensive 
state,  in  which  cases  this  breach  should  be  disputed  with 
the  same  obstinacy  as  those  of  the  other  works. 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  349 

RELATIVE  STRENGTH   OF  THE  GARRISON  AND 
BESIEGING  FORCE. 

As  a  permanent  work  should  force  an  enemy  to  resort  to 
an  attack  by  regular  approaches,  its  garrison  should  be  at 
least  of  sufficient  strength  to  prevent  its  being  carried  by  a 
coup  de  main,  or  open  assault.  The  largest  garrison  will 
depend  upon  the  means  provided  within  the  work  for 
lodging  troops,  and  securing  properly  the  munitions  of 
war  requisite  for  the  number  that  can  be  accommodated 
during  the  presumed  duration  of  the  defence.  Between 
these  two  limits  the  best  military  authorities  estimate  as  a 
medium  garrison,  capable  of  making  a  good  defence,  600 
men  per  front,  or  bastion;  this  force  being  composed  of 
the  different  arms  of  the  service  in  the  proper  proportions 
for  the  duties  required  of  them.  When  the  defences  com- 
prise, besides  the  enceinte,  some  of  the  principal  outworks, 
and  it  is  intended  to  occupy  them  strongly,  with  a  view  to 
an  active,  vigorous  defence,  an  allowance  from  900  to  1,000 
men  should  be  made  per  bastion. 

129. ..With  respect  to  the  quantity  of  artillery  neces- 
sary for  the  armament  of  a  permanent  work,  there  is 
considerable  discrepancy  of  opinion  among  military  writ- 
ers. A  resolute  garrison  might  preserve  a  work  of  tol- 
erable strength  from  a  coup  de  main  without  the  aid  of 
cannon ;  and  an  idea  of  the  largest  amount  of  artillery 
might  be  arrived  at,  hy  supposing  each  front  to  be  armed 
with  as  many  pieces  as  it  can  carry,  with  the  addition  of  a 
suitable  number  of  pieces  in  reserve  to  provide  for  casual- 
ties. But  these  are  inadmissible  extremes,  and  a  medium 
estimate  is  to  allow  3  heavy  guns  and  one  heavy  mortar 
per  front  or  bastion,  with  60  heavy  guns,  20  heavy  mortars 
and  10  stone,  or  light  mortars,  for  the  armament  of  the 
point  of  attack. 

In  estimating  the  amount  of  ammunition,  an  allowance 
of  1,000  rounds  is  made  for  each  gun,  800  rounds  for  each 
mortar,  100  musket  cartridges  per  day  for  each  soldier  on 
guard;  and  300  pounds  of  powder  for  each  mine. 


350  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

130... The  strength  of  the  besieging  force  is  based  upon 
that  of  the  garrison.  The  usual  estimate  is  to  allow,  for 
the  daily  dntj-  of  the  trenches,  at  least  as  many  troops  as 
the  gai'rison,  including  in  this  number  the  men  employed 
in  making  the  trenches.  As  the  service  of  the  besiegers  is 
very  onerous,  the  tour  of  duty  in  the  trenches  should  not 
be  more  frequent  than  once  in  five  or  six  days.  Admit- 
ting this  estimate,  the  besieging  force,  comprising  all  arms, 
should  be  at  least  five  times  as  strong  as  the  garrison. 

131... In  estimating  the  quantity  of  siege  artillery,  as 
man}-  guns  and  mortars  are  allowed  for  the  enfilading, 
counter  and  mortar  batteries  as  the  presumed  armament 
of  the  point  of  attack :  with  an  addition  of  40  or  50 
heavy  guns  for  the  breach  batteries. 

The  medium  allowance  of  ammunition  for  the  artillery 
is  1,000  rounds  for  each  gun,  and  800  for  each  heavy 
mortar. 

132... It  is  hardly  necessary  to  observe  that  the  above 
estimates  are  of  a  very  general  character,  and  are  intro- 
duced here  merelj-  to  give  some  idea  of  the  relative  pro- 
portions in  question.  Before  undertaking  the  siege  of  a 
work,  no  pains  should  be  spared  to  gain  all  the  information 
possible  respecting  the  state  of  its  defences,  and  the  prob- 
able difiiculties  to  be  encountered  in  its  attack,  and  the 
estimates  based  on  these  data  should  be  made  on  the  sup- 
position of  the  work  being  provided  with  all  the  means  of 
a  vigorous  defence. 

Remarks.  In  the  preceding  description  of  the  methods 
of  attack  employed  against  permanent  fortifications,  the 
calculations  for  the  extent  and  strength  of  the  trenches 
and  batteries  have  been  based  upon  the  range  and  effects 
of  the  artillei}^  and  small  arms  which  were  in  general  use 
in  siege  operations  up  to  the  recent  important  changes  and 
improvements  which  have  been  made  in  the  efficacy  of 
arms  and  projectiles  of  every  character.  What  co-rres- 
ponding  changes  in  the  methods  of  attack  will  be  called 
for,  arising  from  these  improvements,  special  experiments 
and  the  experience  derived  from  future  sieges  can  alone 
determine. 


ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS.  351 

From   the   very  ample    official    records  of  the  siege  of 
Sebastopol,  where  the  armament  of  the  defensive  works 
consisted,  in  a  great  measure,  of  the  heaviest  calibre  of 
ships'  guns,  it  wonld  seem  that  no  v^ery  marked  deviations 
were  made,   either  by  the  French   or  English,   from    the 
methods    of   attack    used    in    previous    sieges.      The    first 
parallels    were    commenced    at   ahout    700  to   1,000   yards 
from  the  positions  of  the  defences,  and  the  trenches  were, 
for  the   most  part,  executed  by  the    flying   sap ;    the  full 
sap    being  use»l    by  the    French    sapjiers  alone,  and   only 
when    they  had    approached    very   near    to    the    defensive 
works.     Owing   to   the   peculiar   difficulties  presented  by 
the    character   of   the   ground,  the    defensive    armor   pre- 
scribed for  the  leading  sappers  in  executing  the  full   sap 
was  laid  aside  to  enable  the  men  to  Avork  more  effi?ctively. 
In  the  construction  of  their  batteries,  the  Frencli  appear 
to  have  deviated   only  in   exceptional  cases,  arising  from 
the  nature  of  the  site,  from  the  dimensions  and  construc- 
tions which  had  been  previously  adopted  by  them.     The 
English  engineers,  from  their  experience  in  this  siege,  are 
in  favor  of  thicker  parajicts,  and  a  greater  extent  of  front 
for  each  gun  for  batteries,  particularly  for  the  heavy  cali- 
bres of  ships'   guns  with   which    some   of  their  batteries 
were  armed.      These,  with   a  few  minor  changes  in  the 
details  of  platforms  and  embrasures,  are  the  only  modifi- 
cations in  the  siege  works  of  any  importance  which  the 
results  of  this  memorable  siege  seem  to  have  suggested. 
In  the  defence  of  their  trenches  from  the  frequent  sorties 
of  the   garrison,  the  French,  after  meeting  with  serious 
losses  in   the    earlier   stages    of   the    siege,   from    the  im- 
petuosity   of   their    troops    in    sallying    upon    the    enemy 
beyond  their  trenches,  finally  ado^tted  the  safe   rule  laid 
down  by'Vauban  of  quietly  withdrawing  the  guards  from 
the  portion  of  trenches  upon  which  the  sortie  was  directed, 
witl^the  view  of  assailing  the  enemy  so  soon  as  they  had 
got  within  them  and  whilst  in  a  confused  and  broken  con- 
dition.    This  plan  met  with  full  success,  and  was  found 
most  effectual  in  restraining  the  sorties. 


352  ATTACK  AND  DEFENCE  OF  PERMANENT  WORKS. 

In  tlicir  defensive  works,  which  were  ahnost  entirely  of 
a  temporary  character,  the  Kussians  adopted  for  their  para- 
pets the  ordinary  dimensions  for  resisting  the  heaviest 
calibres.  Although  subjected  to  an  incessant  and  terri- 
ble fire  of  the  heaviest  shij^s'  guns,  with  which  the  be- 
sieger's batteries  were  armed,  these  parapets,  with  such 
dailj'  care  as  could  be  given  in  repairing  their  damages, 
seem  to  have  aftbrded  ample  cover  to  the  garrison  from 
the  direct  fire.  For  cover  from  vertical  fire,  resort  was 
had  to  blindages,  formed,  in  every  sheltered  nook,  with 
the  heavy  timbers  furnished  b}^  the  dock-yards,  which, 
being  covered  with  a  thickness  of  five  or  six  feet  of 
earth,  seem  to  have  answered  completely  their  purposes 
as  shelters  from  the  shocks  of  the  heaviest  shells.  To 
shelter  the  gunners  from  the  embrasure  shot  of  sharp- 
shooters, the  Russians  converted  the  heavy  ropes  of  their 
dismantled  ships  into  a  kind  of  matting,  which  was,  in 
some  cases,  hung  before  the  mouth  of  the  embrasure;  in 
other  cases,  this  matting  was  made  of  a  circular  form, 
with  a  hole  in  the  centre  large  enough  to  admit  the 
chase  of  the  gun,  to  which  it  was  fastened  as  a  screen 
for  the  men  at  the  trail. 

Owing  to  their  ample  garrison,  the  Russians  were  en- 
abled to  take  up  and  fortify  several  strong,  isolated  posi- 
tions, in  advance  of  their  continuous  line  of  works,  after 
the  siege  operations  were  well  under  way.  They  also  used 
with  great  advantage  small  troups-de-loup,  or  pits  for  sharp- 
shooters, in  advance  of  their  line,  from  which  both  the 
workmen  at  the  trenches  and  the  artillerists  of  the  be- 
siegers were  greatly  annoyed.  These  were  in  some  cases 
connected  and  formed  into  a  continuous  trench  of  counter- 
approach,  from  which  they  were  subsequently  driven  only 
after  considerable  loss  to  the  besiegers. 


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